10/24 MS Physics Class and homework due 10/31

Hi folks,

Today we took the time to explore another major force of nature, friction.  Friction is as simple as two things rubbing against one another but, as we discovered with our lab work today, it's not that simple in reality.  It's very hard to predict what kinds of things will have more friction than others.  

For homework this week please answer the following questions based on today's lecture and lab.

1.  What is the definition of friction?

2.  What is the definition of static friction?

3.  What is the definition of kinetic friction?

4.  When I drop a feather and a hammer on Earth, why does the hammer hit first if gravity accelerates all things equally?

5.  Why does a race car have a flat tire without any tread?

6.  Why does the tire on a normal car have tread?

7.  What does the tread on a tire do to help the car?

8.   In the lab we did today with the shoes, what two things were having a "tug-o-war"?

9.  If a shoe moved quickly on the board without the board being lifted much, which one won the tug-of-war.

10.  If a shoe didn't move until the board was lifted quite a bit, which one won the tug-o-war.

11.  What were at least 2 qualities of a shoe that was able to be lifted high before sliding?

12.  Give me an example of static friction.

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Answers

1.  Two objects rubbing against one another.

2.  The friction between something standing still and whatever it is standing on.

3.   The friction between things when at least one is moving.

4.    Air friction slows things down.

5.  Because the tire will have more friction if more tire touches the ground.  

6.  Because a normal road can be wet, muddy, snowy etc. 

7.  The tread is able to channel the water etc away and allow the tire to get through it and touch the road.

8.  Gravity was pulling down while friction was holding the shoe to the board.

9.  Gravity won.

10.  Friction won.

11.  Some possibilities, much of the shoe touched the board, the shoe had a rubber bottom, the shoe was very flat, the shoe was pretty light.

12.  If you push a big box it's hard to get it going but once it gets moving it's easier to push.