Newton’s First and Second Laws of Motion

Chapter 12 Section 2

Newton’s First LawAlso known as The Law of Inertia

O The state of motion of an object does not change as long as the net force acting on the object is zero.

Newton’s 1st lawO An object in motion tends to stay in

motionO In a straight line at a constant speedO And an object at rest tends to stay

at restO Unless acted upon by an outside

force

O It requires a push or pull in order to change an objects state of motion!!!

Newton’s 1st lawO Inertia is the tendency of an object to

resist a change in motion.

O ESA Video

Newton’s 2nd LawO The acceleration of an object is

equal to the force you apply divided by the mass of the object.

Newton's Second Law

O If you apply more force to an object, it accelerates at a higher rate.

O Force is directly proportional to acceleration.

Newton's Second Law

O If an object has more mass it accelerates at a lower rate because mass has inertia.

O The more mass the less acceleration; mass is indirectly proportional to acceleration.

Newton’s 2nd LawO ESA video #2

Newton's Second Law

Newton’s 2nd Law• How much force is needed to accelerate a

1400 kilogram car 2 meters per second/per second?

• Write the formula• F = m x a• Fill in given numbers and units• F = 1400 kg x 2 meters per second/second• Solve for the unknown• 2800 kg-meters/second/second or

2800 N

Practice Problems• 1. What acceleration will result when a 12

N net force applied to a 3 kg object? A 6 kg object?

 • 2. A net force of 16 N causes a mass to

accelerate at a rate of 5 m/s2. Determine the mass.

• 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?

• 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?

Practice Problems-ANSWERS

• 1. What acceleration will result when a 12 N net force applied to a 3 kg object? A 6 kg object?• 4m/s 2; 2m/s 2

•  2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. Determine the mass.• 3.2 kg

• 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?• 66N

• 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?• 9800N

Now Try on your own!!!

Review: O If mass stays the same, and you

INCREASE the force applied to an object, what happens to the acceleration of the object?

O If the force applied to an object stays the same, but the mass is increased, what happens to the acceleration?

Mass Vs. Weight

O Mass is the amount of matter present in an object. Measured in Kg.

O Weight is the effect of gravity on an object’s mass. Measured in NewtonsO Gravity on Earth is 9.8 m/s2 or 9.8 N/Kg)

O Mass does NOT change.O Weight DOES change as gravity changes

O Weight equals mass times the acceleration due to gravity.

O W = m x g

O Remember, gravity is different on other planets!