Download Newton`s Laws of Motion

Newton’s Laws of Motion
1. So you go to Home Depot and pick up a mini-fridge, then place it in the back
of your pickup truck for the ride home. You have no rope, so you simply
place the fridge in the middle of the truck bed. Describe what happens to the
box as you speed up and then slow down.
As you speed up, the box slides to the back of the truck (the box
actually remains at rest as the back of the truck moves); as you slow
down, the box slides to the front of the truck bed (it wants to remain
moving at a constant velocity)
2. The African elephant is the most dangerous animal in Africa because of its
mass. How could you use that to your advantage if an elephant was running
you down? Explain your response.
Zig-zag, or switch directions. The elephant has a very hard time
changing its velocity (b/c of its high mass); you have a much easier
time.
3. If you’re riding in a car that is turning to the left, you will often feel as if you’re
being pulled to the right (towards the outer edge of the car). Explain why this
occurs.
You’re not actually being pulled towards the outside edge of the car;
rather, you remain in place as the car moves around the curve. Your
inertia “forces” you to the outside of the car.
4. Explain what F = ma physically means (do not use the words “equal” or
“times” in your explanation!)
The net force on an object is proportional to the acceleration experienced
by that object. If you double the force on a given object, its acceleration
will double. Also, it takes twice as much force to accelerate an object
twice as massive.
5. During its flight into orbit, a rocket increases its speed. However, it’s
acceleration also increases significantly as it continues firing its thrusters.
Why? (Hint: 90% of the rocket’s mass before takeoff is fuel)
F = ma Assuming F stays constant, decreasing m (as the fuel burns)
will result in a greater acceleration
6. As a sky diver falls faster and faster through the air, does the net force on her
increase, decrease, or remain the same? Does her acceleration increase,
decrease, or stay the same?
Decreases (air resistance increases as speed increases, while gravity
stays constant)
Decreases
7. When you kick a soccer ball or football, the force that your foot applies to the
ball is equal and opposite the force the ball applies on your foot (Newton’s 3 rd
Law). Why does the ball move?
Ball is much less massive than your foot (your foot also stays in place
b/c of friction w/ the ground)
8. Imagine weighing yourself on a bathroom scale while standing next to the
sink. What will happen to the reading on the scale if you push down on the
sink? If you lift up?
If you push down on the sink, the scale reading will decrease; if you lift
up on the sink, the reading will increase