More Third Law ProblemsThe Third Law is helpful in figuring out how things work. In order to analyze things using the Third Law you always want to start by identifying the two key objects involved. Try your hand at these puzzlers…

1. You are standing on the edge of a frozen pond next to a tree. You see a hungry bear nearby. You decide that you need to get away from the bear by backing up, out onto the ice, but the ice is so slippery you can’t get any traction on it. In other words, assume that the friction between you and the ice is negligible. What should you do?

Snack time! Yum.

Now draw and label the forces on these two objects. Pay attention to subscripts, in other words, use them!

Start by identifying two (and only two) key objects:

Gotta back away, but how?

What is the problem with your plan? (Where will you end up?)

What force is responsible for accelerating you away from the bear?

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2. Congratulations. You managed to escape the bear and are now standing on dry pavement. You would like to start walking down the road. Identify the force that will make that possible. Fully label the relevant 3rd Law forces.

3. A rocket is blasting off from the Earth. Sketch and label the 3rd Law forces that are involved in allowing the rocket to rise from the surface of the Earth.

4. Rockets also work in the vacuum of space. Sketch and label the 3rd Law forces that are involved in allowing the rocket to accelerate forward in space.

What force is responsible for accelerating you along the street?

What force is responsible for accelerating the rocket upward away from the Earth?

What force is responsible for accelerating the rocket forward in space?

What are the two key objects?

What are the two key objects?

What are the two key objects?

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