Detecting the Gravitational Field

Ok, sort of a silly experiment I admit. But here’s what we’re going for – there is an invisible force acting on you and the ball. As you will see in later lessons, things don’t change the way they are moving unless a force acts on them. When you jump, the force that we call gravity pulled you back to Earth. When you throw a ball, something invisible acted on the ball forcing it to slow down, turn around, and come back down. Without that force field, you and your ball would be heading out to space right now!
Please login or register to read the rest of this content.

Please login or register to read the rest of this content.

Please login or register to read the rest of this content.


76 Responses to “Detecting the Gravitational Field”
  1. holly_nobl says:

    Would a feather hit the ground at the same time as a bowling ball if dropped from the same height?

  2. Aurora says:

    Gravity is a force that draws objects together, so there’s no real pushing or pulling. As humans, we are attracted to the Earth because it’s the closest, most massive, object to us. The effect of gravity lessens with distance, but it’s never fully gone. So as humans we are probably impacted by the gravity of the moon, the sun, and more.

    And although some think there is no gravity in space, that is not true. Gravity may reach near zero far away from massive objects in space, but you are correct that it’s always there.

  3. Tamara Howard says:

    Is there gravity everywhere? I’m just making sure

  4. Tamara Howard says:

    Does gravity also push down?

  5. Delia Ayer says:

    Yes that makes sense.

  6. Aurora says:

    Ever watch someone jump off a boat into a lake? They dive one way, but what happens to the boat? It goes a little bit in the opposite direction, doesn’t it? Why is that?

    Let me explain. Imagine blowing up a balloon. Blow up an imaginary balloon, but don’t tie it off.

    The instant you let the balloon go, point with your finger the way the air INSIDE the balloon goes. Now point which way the balloon goes. Did you notice that they were equal and opposite? That’s Newton’s third law.

    Here’s another example: Hold your arm out in front of you and push against a wall… the wall is pushing back with the same amount of force (it doesn’t just fall over)!

    That’s Newton’s third law – equal force, opposite direction. The wall matches the size of your push. It doesn’t push more than you do. And when you let go, the wall stops pushing (it doesn’t push harder). That’s what we call a reaction force.

    For every action, there is an equal and opposite reaction. Said another way, forces come in pairs. The thrust from a rocket shoots out the back and the rocket moves forward. Does that make sense? You can read more about it in Unit 1 & 2.

  7. Delia Ayer says:

    Why would we go in the opposit direction of a ball that we tossed in space?

  8. Aurora says:

    That’s the joy of figuring things out, isn’t it? There’s always something new to learn. Why don’t you try the Physics Forums? You can find them here: Try picking up a college freshman or sophomore level textbook on Modern Physics – that should keep you going for while and help you get to where you want to go.

  9. Julianna Richard says:

    Is there any website you can link me to that has more advanced material on relativity? Most of the things on your website are things that I already know. I have been interested in relativity (specifically general relativity) for more than a year now (I’m 13), and my goal is to eventually be able to understand and apply Einstein’s field equations. It’ll be a while, though.

  10. Julianna Richard says:

    I wanted to see if there is a constant ratio between the Schwarzschild radius and the acceleration due to gravity. I assume there is some relation because the both derive from the variables m (Mass) and r (radius).

  11. Aurora says:

    Hi Simon,

    It’s hard to see where you are with your calculations without actually seeing what you’re up to! I am thinking you are asking what the acceleration of an object exactly at the event horizon of a black hole, is that right? You can calculate the Schwarzchild radius using these equations:

    You initially stated that you wanted to calculate the acceleration of an object due to gravity. You can do that by using this equation: g = (GM)/d2 where G is the gravitational constant, approximately 6.674×10-11 N⋅m2/kg2, M is the mass of the larger object, and d is the distance between the CGs of the objects. This equation comes from combining the Universal Gravitation Equation (F=GMm/d2) with Newton’s 2nd Law of Motion F=ma and replacing a=g.

  12. Julianna Richard says:

    This is Simon again. My calculations were wrong. The moon’s gravitation acceleration rate at its Schwarzchild radius was 80 times more than earths.
    My calculations could still be wrong.

  13. Julianna Richard says:

    This is Simon. I am interested in calculating the gravitational acceleration rate for different objects. I’m using the equation g=G*M/r^2.
    I am wondering if there is a constant acceleration rate for all objects at their Schwarzchild radius.
    I tried to calculate the acceleration rate for the earth and the moon at their Schwarzchild radius’ but my results showed that the moon’s acceleration rate was approximately 8 times more than the earth’s. This doesn’t make sense to me.

  14. Julianna Richard says:

    Thanks for your answer. We’re going to just try the experiment again (dropping objects). I’m going to have my older student contact you directly with his specific question with the gravitational force lab and the math involved.

  15. Aurora says:

    Which problem are you working through, and where did you get stuck so I can help?

  16. Julianna Richard says:

    There are several questions here regarding the more advanced lab posted on this page. The helps listed aren’t super helpful. We’re not looking to start an entirely different course of study, but rather to keep younger and older students satisfyingly learning something about this topic, and at a similar pace!
    Basically, if the advanced lab that’s linked here can’t be completed without first taking the physics course or spending hours wading through other material, maybe it shouldn’t be posted here!
    We can’t figure out how to solve this equation when there are several variables involved. Even with the other units, we’re finding ourselves thinking that our lab was not successful or conclusive, and going to youtube for further research.

  17. Aurora says:

    Hi Max! How much gravity you experience depends on how far from the center of the earth you are. If you’re on top of Mount Everest, you going to feel a slightly less gravitational pull than if you were at the bottom of the Grand Canyon. It doesn’t matter where on the surface of the planet or moon you are as it does how far you are from its core.

  18. Amanda Baker says:

    Hi I’m Max I am wondering about gravity if you go to lets say China will that change the force of gravity when you drop a ball
    and if so will it fall faster or slower then in the USA?

  19. Aurora says:

    I’ll have my team connect with you right away!

  20. Yvette Richey says:

    If this is the first unit for 8th grade, why can’t I access all the information?

  21. Aurora says:

    There’s no reason why there couldn’t be more forces, but they would most likely be on the small size, as in smaller than anything we’re able to experimentally test right now. And yes, all of these forces are keeping things together as we know it. Gravity holds galaxies together, electromagnetism holds atoms and molecules together, strong forces hold the nucleus of an atom together…

  22. Susan West says:

    Hi Aurora,

    My 11 year old daughter Lucy and I are trying your program out for the first time, and this lesson is sparking off some interesting questions.

    She asks: How do we know there are only 4 forces? Could there be forces we don’t know about acting in such things as black holes?

    Also, is there a force keeping everything within the boundaries of this universe?

  23. Aurora says:

    Probably not – insects have this amazing ability to “float” (sort of) to the ground, because they are so light for their size (surface area) so they have more air resistance and are more buoyant in our atmosphere. Their terminal velocity isn’t fast enough to kill them.

  24. Terria Burton says:

    If you drop an ant off the Eiffel Tower will it die? Kenlee

  25. Aurora says:

    Find experiments on velocity and acceleration calculations in this section here:

  26. Claudia Evans says:

    Forget that question for now! My son asked it, and I have not had a chance to read through all the previous comments. He is not finding a video or reading on how to calculate initial velocity and acceleration of toss.

  27. Claudia Evans says:

    How can my son do this experiment at the high school level?

  28. Aurora says:

    I am sorry you’re having trouble! We are actually reworking the navigation so it’s easier to find what you need on the site quicker and faster. In the meantime, let me show you how to access the the upper level HS content from the Grade Level side:

    and here’s the section in Physics:

    The first lesson starts here:

    and here’s the first download you’ll want to review that has the order and sequence of the lessons near the front:
    The PDF download has a schedule for working through the program.

    Yes, the acceleration of gravity is 9.8m/s2 toward the center of the earth.

    Let me know if you have more questions so I can help!


  29. Esther Despain says:

    I am having the same problem as Heather:

    “In Unit 1: Lesson 1 on Detecting the Gravitational Field…I wanted my daughter (9th Grade) to do the ‘advanced experiment’ …where the acceleration is calculated from the following equations:…”

    And your response just took us to the general Advanced Physics page not to a specific lesson or example. I do not have time to wade through everything to find the clarification needed for the advanced labs. My 10th grader is trying to work his way through the Advanced Physics, but is becoming very frustrated.

    After some discussion with my 8th and 10th graders, we concluded that the acceleration was probably -9.8 m/s2 (toward earth). Is this correct?

    An example on the “Advanced Detecting Gravitational Field” Worksheet would be very helpful for those of us who are linking from the Unit One “Forces” Experiment Area.

    I am trying to teach multiple age groups and have everyone participate at their own level, but if the advanced labs that are linked are too ambiguous, it is not working for us. Is it always going to be this difficult and frustrating to incorporate all levels? Is there a place that correlates the advanced physics with the normal units at a glance? I understand it cannot be a 1:1 correlation as the advanced physics course will spend more time and detail on the concepts presented in the units, but a correlation table would be helpful.
    I really wanted this to work for us, I love the hands-on approach and was even going to purchase a Diamond Science Mastery, but am really having second thoughts after trying to make this work for the past couple of weeks.

  30. Aurora says:

    Where did you find the chapter in question? I am not seeing it with this experiment. Can you provide the URL?

  31. Michelle Palmer says:

    Hi I’m confused as to why there is a Chapter 4 Force and Motion that goes with Unit 1. Is this from two different sources? What is the Chapter 4 from? A textbook? Are the Units from a different textbook?

    Thank you.

  32. Shirley Caron says:

    Why does the hair color and texture matter in electromagnetic forces???

  33. Aurora says:

    I just tried it in IE… here’s the direct link until we can figure this out.

    So sorry about that!

  34. cheesebloxs says:

    Some of the links work for me. But, for example, the link in this section (Detecting the Gravitational Field), the link for

    “Download Student Worksheets and Exercises” does not work in Safari or in Chrome on my laptop. Thanks.

  35. cheesebloxs says:

    I am using Safari on my iphone and ipad.

  36. Aurora says:

    Yes – they do! What browser are you having trouble with? They work here in Google Chrome, Firefox and IE.

  37. cheesebloxs says:

    Do the links for Student Worksheets and Exercises work? Thanks.

  38. Aurora says:

    Wonderful! So glad you’ve found us. The shopping list can be found on the main page for the unit on the right. For Unit 1:

    Loop on the right where it says “Shopping List” on the 3rd link down. When you click on this, the same shopping list as in the download pops up, but this time the links to order the hard to find stuff are all active.

    Note: Since these links take you off-site to other companies, occasionally there’s a link that’s broken or missing. If you ever find one, please let us know so we can fix it right away with a new company.

  39. Jana Williams says:

    Aurora, love your program. Have a question. In the shopping list for the mechanics lesson
    You mention links to online ordering of supplies but I don’t see any.
    Where are they? Thanks Jana and Joey

  40. Aurora says:

    Yes that is the general idea. Gravity is only an attractive force.

  41. Laura Swick says:

    Gravity is always pulling to the center. So on earth, we are always pulled towards the center of it. Is this a correct definition for gravity?

  42. Aurora says:

    Hi Heather,

    I apologize for missing your question and not getting you an immediate answer! There’s actually an entire section that details this very clearly that is located here:

    Depending on how much physics she’s had, she can jump right into the section on projectile motion here:

    or if she hasn’t had any at all, she’ll want to start at the beginning, which is 1D kinematics.

    Hope this help! Again, sorry for the delay. 🙂

  43. Heather Sebring says:

    This video helps clear up a lot of misconceptions about this gravity lesson that can occur…

  44. Heather Sebring says:

    In Unit 1: Lesson 1 on Detecting the Gravitational Field…I wanted my daughter (9th Grade) to do the ‘advanced experiment’ …where the acceleration is calculated from the following equations:

    Vf = Vi + at
    Vi = -a(1/2t)
    Yf = Yi + Vit + 1/2at^2
    Yf = Vi (1/2t) + 1/2a(1/2t)^
    Vf^2 = Vi^2 + 2a(Yf – Yi)
    a = Vf^2/ (2Yf)

    I understand how to get the travel time…just not the initial or final velocity and maximum height….? Where the experimenter simply records the time after “toss the ball directly up as high as you can”.

    I have no way of measuring the initial velocity (how fast the ball goes up??) or is that zero since it started from a stand still…also how to measure how high (maximum height) of the ball if each throw is as high up as one can get it – how would one really measure that?

    I do not know how to explain how my child should “fill out the table on the first page with the corresponding toss accelerations” if the only value we can put in is total travel time (sec) from the timer??? Even if we use the KNOWN value for acceleration – we are still missing the initial velocity and maximum height …and the point was to calculate acceleration from this experiment…not used predetermined values right?

    Please help….this is our first real experiment and we are already frustrated. Getting the concepts is fun and a breeze …just not making the math proof of it work!

  45. Aurora says:

    Interesting question. Gravity is a force that pulls you downward, and as long as there’s a mass, there’s gravity. We don’t know why gravity is, we just know it’s there. You can’t have a planet without gravity, and the amount of gravity a planet has depends on the mass of the planet (the size and how heavy it is).

  46. Amy Chin says:

    Hi I’m Colin Chin

    Does gravity wear off and more comes in or does it never wear off?

  47. Aurora says:

    Yes, you’re brain will turn into a pretzel if you’re not thinking about this one clearly. 🙂 There are several misconceptions about gravity. Let me show you:

    When you drop a golf ball and a ping pong ball from the same height, what happens? (If you haven’t tried this, you need to for this next part to make sense…)

    You’ll find that both objects hit the ground at the same time! This means that gravity accelerates both items equally and they hit the ground at the same time.

    (By the way, any two objects will do this. But here’s the catch…)

    What if you drop a feather and a ball at the same time? There is one thing that will change the results and that is air resistance. The bigger, lighter and fluffier something is, the more air resistance can affect it and so it will fall more slowly. Air resistance is a type of friction which we will be talking about later in Lesson 3 of Unit 1.

    (If you removed air resistance, all objects would hit the ground at the same time. Where can you remove air resistance? The moon! One of the Apollo missions actually did this. An astronaut dropped a feather and a hammer at the same time and indeed, both fell at the same rate of speed and hit the surface of the moon at the same time. If you haven’t seen this video on this exact experiment, check it out.)

    With me so far? Now think about this: Which will hit the ground first (if dropped from the same height) a bowling ball or a tennis ball?

    Did you say the bowling ball? It’s common sense to think that the heavier object falls faster. Unfortunately, this time common sense isn’t right. Gravity accelerates all things equally. In other words, gravity makes all things speed up or slow down at the same RATE.

    Ok, so now onto your question…

    Gravity accelerates all things equally, not gravity pulls on all things equally. Gravity does pull harder on some things than on other things. This is why I weigh more than a dog. I am made of more stuff (I have more atoms) than the average dog, so gravity pulls on me more.

    If you take a set of different-sized and weights of objects (like a cotton ball, marble, fork, paperclip, paper plate), and drop them all from the same height (way up high), could you predict which one hits the ground first? Some of them would reached their terminal velocity (objects that can’t gain any more speed because the air resistance pushing against that something is equal to the force of gravity pulling down) soon after you let them go and they fall all the way to the ground at that same constant velocity. It’s a balance between the air resistance and the pull of gravity. This is why feathers drop so much more slowly than bowling balls. A feather has a very large amount of air resistance and gravity pulls very lightly on it (the feather is very light).

    Hops this helps!

  48. Helga White says:

    I need help understanding the relationship between these two statements:

    1. Gravity accelerates all things equally – all things speed up the same amount as they fall. Gravity doesn’t care what size things are or whether they are moving, all things accelerate toward Earth at the same rate of speed.


    2. Gravity does pull on things differently – it is pulling greater on objects that weigh more.

    If it is pulling greater on objects that weigh more, why aren’t they speeding up?

  49. Aurora says:

    Hi Logan and Rema! It sounds like you were able to magnetize your nail just fine. Sometimes when students rub vigorously back and forth, they don’t do it in a straight line so the domains get all jumbled up inside the nail and it doesn’t work, but it sounds like you were careful and it lined up along the axis, so good job!

    As for your q about friction: the interaction between an object and the air does affect the fall rate – it’s called drag, or air resistance. The air has to move out of the way for larger objects versus smaller objects. You can feel this effect if you roll down the window in your car when your parents are driving, and try facing your palm toward the wind, and then facing palm down to the ground. There’s a difference in the amount of force you feel as the wind either slips over your hand easily if it’s palm-down, or hits your hand if your palm is facing the oncoming air. You’ll need to drop your objects at exactly the same time from a larger height (two story windows come to mind, if you’re careful) to see the difference visually.

    Parachutes have a large cross-sectional area that the wind sees compared to the area it sees from a human (which is going to be only the width and thickness of your waist, not your height, as a parachuter is falling toward the ground and looks more like a slim pencil to the air). The parachute will slow down the paracheter since it has way more drag than a person does falling through the air. The parachuter acts as an anchor (weight) to the end of the parachute, keeping it open and in it’s maximum size. Does that make sense?

  50. Rema Gurunathan says:

    Hi Aurora,
    I am Logan and I am in Year 4 (Australia). Me and my sister did the experiment “detecting the gravitational Field” and I am wondering why does the friction between the object and the air not affect the fall rate of the object. I tried dropping a book and a ball. Even though gravity has the same effect, I would have thought that the wider surface of the book would make it drop later due to friction. How come the friction works with parachutes?

  51. Melissa Johns says:

    Today we did the “Detecting the Gravitational Field” experiment. When testing the Mass, our golf ball and ping pong ball hit at the same time. When testing the size, the paper wad and flat piece of paper hit at different times.
    We then looked at the Exercise questions and answers. This is where I got confused. Question #3 asks “did changing the variable affect the rate of falling? Your answer is “No, it appears that gravity affects all objects the same”, but it seems to me that changing the variable did affect the rate of falling.

  52. Brenda Jymison says:

    In one of our experiments our variables were a sheet of toilet paper and a pencil. As we guessed, the pencil hit the ground first, as the sheet of toilet paper “floated” to the ground. Is the scientific explanation for this happening similiar to the helium balloon question above in that the sheet of tissue “gets air” below it?

  53. Aurora says:

    It depends on the range you’re talking about. On large scales, gravity is the “strongest” of them all when you look at things large-scale structures like black holes and galaxies. However, if you list the four forces just by strength, then gravity is the weakest of them all. You can see this for yourself when you notice that it takes an entire planet to keep a sheet of paper on a desk, but if you bring a charged balloon (a balloon you rubbed on your head to build up a static electric field), you can get the paper to stick to the balloon (electromagnetic force).

    Inside an atom, the strong force is the strongest (and it’s also the strongest if you measure them out and list them just by strength). The strong force is the force that holds the nucleus together (if you think about it, there’s really no reason for protons and neutrons to want to stay together without it), and it’s range is the diameter of a medium sized atomic nucleus.

    The electromagnetic force holds the atoms and molecules together, and it has an infinite range (like gravity) but is only 1% as strong as the strong force. Some people consider this one is the strongest on a scale larger than an atom but smaller than a galaxy.

    The weak force has only a range of 0.1% of a proton diameter, which is smaller than the range of the strong force, but it’s actually stronger than the electromagnetic force when you’re operating within its range.

    Long story short: you can’t just look at which one is strongest based only on field strength. You also have to look at the range that the force is active within. Hope this helps!

  54. Lisa Niedermeyer says:

    Which force is the weakest?

  55. Mary Silvernagel says:

    Hi, Could you please tell me which is greater, the weak nuclear force, or the electromagnetic force?


  56. Shae Tebbetts says:

    Good thing!

  57. Aurora says:

    I understand your question now. No, our own personal gravitational field is not measurable or attractive enough to move objects close to it… things have to be planet-size before we’re able to detect it.

  58. Shae Tebbetts says:

    I guess I’m wondering about this statement:
    “What we do know is that all bodies, from small atoms and molecules to gigantic stars, have a gravitational field. The more massive the body, the larger its gravitational field.”

    I understand that our mass it too small to create a significant gravitational pull for most objects, but I wondered if it was enough to attract small things like bacteria or atoms.

  59. Aurora says:

    I am not sure what you’re referring to – can you please explain a little more? The gravitational field we experience here on Earth is strong enough to keep us (and bacteria) from floating off into space, but on the small scale of things, it’s the weakest of the four forces.

  60. Shae Tebbetts says:

    Is our gravitational field strong enough to attract bacteria? or atoms?

  61. Cheryl Ramirez says:

    never mind! found them!

  62. Cheryl Ramirez says:

    Same question as Kimberly….where are the questions for Unit 1 Mechanics.

  63. Aurora says:

    Well, since that’s the case, you’ll want to be sure to use your safety goggles. I hear Cyron52b has titanic plastic dust storms. 🙂

  64. Natalie Roth-Corti says:

    You do realize that i cannot do this experiment on Cyron52b, its made of plastic explosive and has a very strong gravitational field. Boom.

  65. Aurora says:

    At this time, scientists haven’t discovered it yet. Not everything in science is symmetrical. What scientists are really looking for now is the mysterious particles that gives stuff its “mass” (higgs-boson) and convey the gravitational force (named the ‘graviton’). There’s more details about this in Unit 7 Lesson 1: Particle Physics.

  66. Lynn Glasheen says:

    Do you think there might be a repulsive side to gravity that we have not discovered yet?

  67. Aurora says:

    Yes atoms have a gravitational force field but this is not why they are held together. Gravity between individual atoms is extremely weak compared to the force of chemical and physical bonds. These bonds are what keep atoms from escaping and leaving their other atom friends behind. Great question!

  68. RUTH HAYNES says:

    Here is my 6-year-old boy’s take on this lesson. “So God’s gravity gets under my feet and pulls me down to the ground. So I get that part. I get what they’re saying.” Then he kept going on and on and on…”Mommy, are you listening?”

  69. Gennifer Hogan says:

    Atticus wants to know: if atoms have a gravitational field does that mean that gravity is holding us together?
    Thank you

  70. Aurora says:

    That’s a great question! Gravity does pull on the helium inside the balloon, however the air in our atmosphere is denser than helium, so gravity will pull on the air harder than it pulls on the helium. When this happens the air sinks below the helium, and the helium floats until it reaches a point in the atmosphere where it has the same density as the thinner atmosphere. That’s where you’ll find escaped helium balloons hanging out. 🙂

  71. Melissa Wilson says:

    My 7 y.o. wants to know why gravity doesn’t act on a balloon? If gravity acts on all objects on earth, how come it isn’t strong enough to pull down a helium balloon? I feel like I really should know the answer to that, and obviously it has to do with the helium, but why doesn’t gravity act on gases? I don’t really have the “science” answer being a liberal arts person myself.

  72. Marvette Owens-Freeman says:

    Thanks Aurora that helped me very much.


  73. Aurora says:

    There’s only two you really need to worry about: gravitational and electromagnetic. By doing the experiments in this section, you’ll get experience with both and have a working understanding of both… which is more important than just plain memorizing. Go easy on yourself and have fun with the experiments – it’s more important to train your brain to ask questions and notice what’s going on than trying to remember vocabulary words – at least in the long run. The terminology and official wording of the physical laws and forces will come to you with time. Your job now is just to investigate, discover, and enjoy the experience. Does that make sense?

  74. Marvette Owens-Freeman says:

    Is there anyway I can remeber the four forces.

    thanks Aurora

  75. Aurora says:

    Do you see in the upper right corner how it says Force Video, Force Reading, Force Experiments, and Force Exercises? Click on Force Exercises to get where you want to go.

  76. Kimberly Prewitt says:

    where are the questions for this unit?

Have a question?

Tell us what you're thinking...

You must be logged in to post a comment.