11. The truck is in motion . What is the force that causes it to stop? The push of the stopped car. The car is at rest . What is the force that causes it to move? The push of the truck.
12. What about the ladder on top of the truck? The ladder is in motion because the truck is in motion. When the truck stops, the ladder stays in motion. The truck is stopped by the force of the car, but the ladder is not. What force stops the ladder? Gravity .
13. The truck is in motion , the car is at rest . How do each of these vehicles accelerate ? The truck stops moving. The car starts moving. Which one will be the hardest to accelerate ? The truck because it has the most mass.
14. Why does the car move [accelerate] when it is hit by the truck? The heavy and moving truck has more force than the small, at rest car. Why does the truck stop moving when it hits the car? The force of the car pushing back on the truck, plus the force of friction between the massive truck and the road slow down, the stop the truck.
15. The truck hits the car. An action force stops the truck. What is the equal and opposite reaction force? The force that pushes the car forward.
![First we need to define the word FORCE : ,[object Object],[object Object],[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)