Driving Home Newton's Laws of Motion Automobiles, baseballs, skateboards and bicycles -- the world is full of things that are in motion. Centuries ago the British physicist Sir Isaac Newton stated three laws that describe the ways in which things move. These are Newton's three laws of motion: • The first law: Unless acted upon by an outside force, a body at rest tends to stay at rest, and a body in motion tends to stay in motion. • The second law: Acceleration is equal to the net force acting on a body divided by its mass. • The third law: For every action force there is an equal and opposite reaction force. A driver starts her car and steps on the gas pedal. The car gradually accelerates to 50 km/hr. A few minutes later, the driver suddenly slams on the brakes to avoid hitting a box in the road. As the car comes to a stop, the driver's body appears to lurch forward in the seat until it is restrained by the seat belt.

Driving Home Newton's Laws of Motion

Automobiles, baseballs, skateboards and bicycles -- the world is full of things that are in motion.

Centuries ago the British physicist Sir Isaac Newton stated three laws that describe the ways in which things move. These are Newton's three laws of motion:

•     The first law: Unless acted upon by an outside force, a body at rest tends to stay at rest, and a body in motion tends to stay in motion.     (back to Q. 1)

•     The second law: Acceleration is equal to the net force acting on a body divided by its mass.     (back to Q. 1)

•     The third law: For every action force there is an equal and opposite reaction force. (back to Q. 1)

A driver starts her car and steps on the gas pedal. The car gradually accelerates to 50 km/hr. A few minutes later, the driver suddenly slams on the brakes to avoid hitting a box in the road. As the car comes to a stop, the driver's body appears to lurch forward in the seat until it is restrained by the seat belt.      (Back to Q. 1 & Q. 2)

Choose the correct answer for each question.


1	Which law best explains why the driver's body appears to lurch forward when the brakes are suddenly applied?
		Newton's first law
		Newton's second law
		Newton's third law
		The law of gravity


2	Use the following graphs to answer this question. Which graph best matches the motion of the car described in the paragraph above?