Skateboard Lab

 

Situation #1:  A small person and a larger person are on skateboards facing each other.  They are currently standing still.  They are holding hands and are about to “push” away from one another.

 

1.     How does the force the small person exerts on the large person compare with the force that the large person exerts on the small person?  In other words, who is producing the greater force.  How can you prove your conclusion (what instrument would you use to measure the forces?)

 

2. The people “push” off from each other.  Who moves away faster?  Who moves away further?  Why does this happen?  Use Newton’s 2nd law (F=ma) to explain yourself.

 

 

Situation #2: A large person (P1) on a skateboard collides with a person one-half his mass (P2).  The smaller person was initially at rest on his skateboard. He grabs his hands as he collides with him, and they move off together without falling.

 

 

3.  During the collision, how does the force that the larger person exerts on the smaller person compare with the force that the smaller person exerts on the larger person?

 

4.  After they collide, what will happen to their combined speed?  Will they a) stop completely  b) go off at a speed less than the P1’s original speed   c) go off at a speed greater than the P1’s original speed.

Situation #3: Now the larger person (P1) on the skateboard approaches the smaller person, but the smaller person (P2) is moving away from him (at a slower speed) than he is moving.  When the larger person reaches the smaller person, he grabs his hands and they go off together.

 

5.  During the collision, how does the force that the larger person exerts on the smaller person compare with the force that the smaller person exerts on the larger person?

 

6.  After they collide, what will happen to their combined speed?  Will they a) stop completely  b) go off at a speed less than P1’s original speed  and less than P2’s original speed.  c) go off at a speed greater than P1’s original speed and greater than P2’s original speed  d) go off at a speed less than P1’s original speed but greater than P2’soriginal speed

 

Situation #4:  Now the larger person (P1) approaches the smaller person (P2) who is completely stopped on his skateboard but is facing him with his hands outstretched.  P1  hits the hands of P2 and DOES NOT hold their hands.  Rather P2 is pushed back from the force of P1.

 

7.  If P2 keeps his arms and hands rigid (so that the force of the impact DOES NOT make him bend his elbows), what do you think will happen to P1 and P2?

 

8.  If P2 allows his arms to bend at the elbows upon collision, what do you think will happen to P1 and P2?

 

Situation #5:  A person is standing on a skateboard (minding their own business).

 

9.  Suddenly, someone throws a heavy object (like a ball) to them – they catch the ball.  What happens to the person on the skateboard?  (SAFETY FIRST!!!!!!!:  when you try this, make sure you have someone standing BEHIND the person on the skateboard who can catch them if they begin to fall.)

 

10.  The person on the skateboard is completely stopped and is holding a heavy object (like a ball).  He throws the ball to a person standing nearby.  What happens to the person on the skateboard?  (again, be ready to catch the person on the skateboard)

 

 

 

 

 

 

 

 

 

 

 

 

Classroom Demonstration:

 

Look at the following diagram of an in-class demonstration which illustrates situation #3 Instead of people on skateboards, however, we will use carts moving along a track. Below is a picture of the situation. The double cart represents the man and the single cart at rest represents the woman. What happens?