1. Press "Start". A force is pulling the block to the right. This force is steadily increasing. On the vertical axis, you can see the force of friction.
2. What can you say about the force of friction when the object is not moving?
3. What can you say about the force of friction when the object is moving?
4. Which one of these friction forces (static or dynamic) is greater?

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Click Start and observe what happens. The forcing, F, pushing the block will steadily increase until the block moves.

Explain the occurrence using the concepts of static and dynamic friction.

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1. What happens to the air resistance as the object speeds up?
2. What happens to the weight when the object speeds up?
3. What happens to the net force when the object speeds up?
4. What is the acceleration of the object when it starts?
5. What is the acceleration of the object "in the end"?

1. Press the play button.
2. Let the skydiver fall about 80% of the distance and then press "Parachute"

Look at the middle graph (velocity - time). What does it look like just before opening the parachute? What can you say about the forces on the skydiver at this time?

Look at the first graph (displacement - time). The slope is constant just before opening the parachute. Explain the constant slope by referring to the forces on the skydiver and the middle graph just before opening the parachute.

After opening the parachute the velocity decreases. Explain this decrease by referring to the forces on the skydiver.

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                                                       Static friction                                                                                      Dynamic friction

                 .                             

  From static to dynamic friction 

          No air resistance                                                 Air resistance    

What is the force A shown? Weight or Net force? Why?

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Change the angle of the tension. Why does the force of friction also change?

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                        Same angular velocity                                                     Same speed

.    

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Same speed - What can you say about the forces?

Same force - What can you say about the speeds?

This simulation assumes that the ball is traveling at uniform speed (not accelerating)

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1. Click "Animation On" and "Side View".

2. Increase the velocity of the ball from the slider. 

What happens? Why?

If you were able to increase it further, could you make the ball spin in a fully horizontal plane? Why yes/no?

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