Motion Lab: Inertia, Net Force, and How Fast
The three simulations are on this page. Work down the page and use them as you go. Nothing here is calculated. Set what you are told to set, watch, and write down what you see and what the panel tells you.
1. Warm-up: take the rubbing away5 points
A puck on a long track. The push button gives exactly the same push every time. The roughness slider decides how fast the surface takes the motion away, and it goes all the way down to nothing.
Set the roughness slider all the way down to nothing and press Same push. Watch what happens to the speed and to Where it stops. Then slide the roughness back up and push again. Write one sentence saying what the rough surface does that the smooth one does not.5 pts
2. The same push, four different pucks15 points
The same simulation as Part 1, above. Leave the roughness at the middle mark and leave the Moon box unticked until the last question.
(a)Move the mass slider from 1 kg up to 6 kg, pressing Same push at each setting. Say what happens to Speed right after the push as the puck gets heavier, and say which puck was the hardest one to get moving.7 pts
(b)Fill the table in. Then set the mass to 3 kg and tick Put the track on the Moon. Say which of the two numbers in your table changes on the Moon and which one does not, and say what that tells you about mass and weight.8 pts
| Mass of the puck | Speed right after the push (m/s) | Weight on the Earth (N) |
|---|---|---|
| 1 kg | ||
| 2 kg | ||
| 3 kg | ||
| 6 kg |
3. Two ropes on one block15 points
One block on a floor with nothing to rub on, and a rope on each side. The two sliders set how hard each rope is pulled. The small box in the corner shows all four forces at once.
(a)Set both pulls to 20 N and press Reset. Say what the block does and what the panel gives for the net force. Now press Give it a nudge and say what the block does after that, and what the net force is while it does it.7 pts
(b)Press Reset, then fill the table in, resetting before each row. Then say what the panel gives for the net force up and down, why that number is what it is, and what has to be true of the sideways forces for the speed to change at all.8 pts
| The two pulls | Net force, sideways | What the block does from rest |
|---|---|---|
| 20 N and 20 N | ||
| 20 N and 30 N | ||
| 40 N and 25 N | ||
| 45 N and 45 N |
4. How fast are you going?15 points
A moving walkway with you on it. One slider moves the walkway, the other is how fast you walk along it. A negative walking speed means walking back against the way the walkway is carrying you. Each run lasts ten seconds.
(a)Set the walkway to 2.0 m/s and your walking to 0.0, and run it. Then set the walkway to 0.0 and your walking to 2.0, and run it again. The two runs give the same Speed compared with the ground. Say what is different between them, and what somebody standing on the walkway beside you would say about your speed in each one.7 pts
(b)Fill the table in, pressing Run for each row. Then find the setting where you are walking hard and getting nowhere over the ground, and explain how you can be moving and not moving at the same moment.8 pts
| Walkway and walking | Speed compared with the walkway | Speed compared with the ground | Distance over the ground in 10 s |
|---|---|---|---|
| 2.0 and 0.0 | |||
| 2.0 and 1.0 | |||
| 2.0 and −2.0 | |||
| 0.0 and 1.5 |