Ch

ap

ter

2:

Lesson

3

The acceleration of an object is equal to the net force exerted on the object divided by

the object’s mass.

Force =

Acceleration =

The acceleration due to gravity on earth =

Newton’s 2nd Law of Motion

9.8 m/s2

Mass x Acceleration

ForceMass

If you want to find…

And you know… Then the formula you would use is…

Acceleration (a)

Net Force (F)

Mass (m)

Three Forms of Newton’s 2nd Law

Net Force (F) and mass (m)

Acceleration (a) and mass (m)

Net Force (F) and acceleration (a)

Identify the information you are given◦ Look at the units◦ Unit for Force –

Remember: is a force due to If the problem asks you to solve for weight you need

to identify the acceleration due to gravity for your given location.

◦ Unit for Acceleration – ◦ Unit for Mass –

Use the appropriate formula

Units for solving for Newton’s 2nd Law

Newton (N)

m/s2

Kg or g

Weight gravity

A man has a mass of 66kg on Earth. What is his weight?

Practice Problem

Johnny hits the baseball with 100N of force. The baseball has a mass of 14.2kg. Identify the acceleration of the baseball.

Practice Problem

A girl on roller skates with a mass of 55kg accelerates at a rate of 2m/s2. What is her force?

Practice Problem

Richie went fishing with his dad. He felt a bite on his line and started reeling the fish in with a force of 201N. The fishing line was moving at an acceleration of 22m/s2. What was the mass of the fish that he reeled in?

Practice Problem

An object at REST Balanced Force The force exerted

by the is to

Unbalanced Force The force exerted by gravity is than air resistance.

GREATER HAND

EQUAL THE FORCE OF GRAVITY

Unbalanced forces cause objects to

An object in MOTION

ACCELERATE

1. Increase Speed2. Decrease Speed3. Change Direction

Part I: Acceleration Depends on Mass

Acceleration as its mass

Acceleration as mass

Example: You are pushing a shopping cart at the grocery store. At the beginning of your shopping trip, you exert a small force on the cart to accelerate it. (smaller mass = greater acceleration)

Exert the same amount of force when the cart is full and the cart will not accelerate as much. (greater mass = smaller acceleration)

http://www2.hawaii.edu/~kobatake/secondlaw4.html

decreases increases

increases decreasesAcceleration and mass are inversely related

Part II: Acceleration Depends on ForceAcceleration as the force on it

Acceleration as the force on it

Example: When pushing the full shopping cart, if you push harder (greater force), the cart will move faster.

If you push the full shopping cart with less force, the cart will move slower.

**The acceleration is always in the as the force applied. The shopping cart moved forward because the push was in a forward direction

increases increases

decreases decreases

Acceleration and force are directly related

same direction

We know that objects with different masses accelerate to the ground

However, because of the 2nd Law we know that they don’t hit the ground with the same

F = ma

98 N = 10 kg x 9.8 m/s/s

F = ma

9.8 N = 1 kg x 9.8 m/s/s

at the same rate.

force.

Newton’s second law explains why objects fall to Earth with the same acceleration (9.8 m/s)

Less mass

Less Gravitational force

Less inertia = easier to move

More mass

More Gravitational force

More inertia = harder to move

ConstantType of

Relationship

Force

Mass Increases

Acceleration ________

Mass ___________

Acceleration Increases

Mass

Force Increases

Acceleration ________

Force ____________

Acceleration Decreases

Acceleration

Force Increases

Mass ___________

Force ____________

Mass Decreases

Decreases

Increases

Increases

Inverse

Direct

Direct

Decreases

Decreases

Decreases

Any motion in which an object is moving along a curved path.

For example: A rider on a merry-go-round moves in a circle. This type of motion is called

If you are in circular motion, your of motion is constantly

This means you are constantly

Circular Motion

direction

Circular motion

accelerating

changing

Centripetal Force A force that causes an object to move in a

circular path

If you are constantly accelerating there must be a force acting on you

The force exerted is the and always points to the center of the circle.

at all times

centripetal force

All requires a

Because the force acts toward the of the circular path, the acceleration must also be toward the

CIRCULAR MOTION CENTRIPETAL FORCE

CENTER

CENTER