When a boulder and a pebble are dropped, why does the pebble pick ...

[Yolanda]

When a boulder and a pebble are dropped, why does the pebble pick up speed as quickly as the boulder, even though less gravity acts on it? In other words, why do both accelerate equally?
 
  What will be an ideal response?

Question 2

A physicist says that a car accelerating along a level road is being propelled by the road. Defend this statement.
 
  What will be an ideal response?

[Carissamariew]

Answer to Question 1

Answer: Acceleration depends not only on the force of gravity, but also on the mass. If the boulder is fifty times heavier than the pebble, it also has fifty times as much mass. So in accord with Newton's second law, fifty times as much force on fifty times as much mass gives the same acceleration as one-fiftieth the force on one-fiftieth the mass on the pebble. Both boulder and pebble accelerate equally. If air resistance affects motion, then the accelerations will not be equal.

Answer to Question 2

Answer: It's true. The tires are made to rotate by the engine, and the tire surfaces are the only points of contact with the road. The turning tires push backward on the road. Interestingly, the tires can only push backward on the road if the road simultaneously pushes forward on the tires. This forward force is the only force that propels the car along the road. Air resistance occurs also, partly counteracting the propulsion by the road.

[Yolanda]

TY

[Carissamariew]

You're welcome