Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!
Here’s printer-friendly versions of the exercises and answers for you to print out: Simply click here for K-8 and here for K-12.
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Answers to Energy Exercises:
1. Matter and energy.
2. The ability of an object or system to do work on another object or system. Energy is defined in the physics books as the ability to do work.
3. Work is moving an object against a force over a distance. Work = force x distance
4. Yes. The chair has been moved a distance, against the force of gravity.
5. Nope, the chair moves a distance, but it moves with the force of gravity. Work is moving something a distance against a force. In this case, the chair does not move against a force. No work is done.
6. Nope again! There’s no distance moved so…no work done.
7. Joules and calories.
8. The amount of work done in a given amount of time. Power = work divided by time.
9. Watts and horsepower.
10. The sun. You are powered by the sun!
Answers to Simple Machines/Levers Exercises
1. The six machines are the inclined plane, the wheel and axle, the lever, the pulley, the wedge, and the screw.
2. The distance that the effort moves is much greater than the distance the load moves.
3. A first-class lever is a lever in which the fulcrum is located in between the effort and the load. Some examples are see-saw, a hammer (when it’s used to pull nails), scissors, and pliers.
4. In a second-class lever, the load is between the fulcrum and the effort. Some examples are a wheel-barrow, a door, a stapler, and a nut-cracker.
5. The third-class lever has the effort between the load and the fulcrum. A few examples of this are tweezers, fishing rods, your jaw, and your arm
For Advanced Students:
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Answers to Energy Calculations
1. work = force x distance so
work = 1 newton x 2 meters
work = 2 Joules
2. Power = work/time
power = 2/180
power = .01 Watts
3. work = force x distance
work = 1000 x 30
work = 30,000 Joules (go Bob!)
4. power = work x time
power = 30,000/5
power = 6000 Watts (Wow! Big Bob!)
5. 6000 Watts x .001 = 6 horsepower (No Viper, but pretty impressive!)
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Thank you, that makes sense now!
Yes, gravity can do work, but since gravity and the chair’s movement are in the same direction, there’s no work done on the chair by gravity. If the chair was moving upwards against the pull of gravity, then gravity would be doing work on the chair.
In this case, you could say that there is work done by friction of the air molecules against the chair as it falls through the atmosphere, because friction forces oppose the motion.
The answer to question 5 (in the energy exercise) says that no work was being done on the chair while it’s falling because the chair was not being moved against a force. I was wondering, isn’t gravity working against air resistance to cause the chair to fall? And if so isn’t gravity moving the chair a distance (from the top of the roof to the ground) against a force (air resistance)?