Section 2.2 Force and mass determine

acceleration.

• ___________________________ states that the acceleration of an object increases with increased force and decreases with increased mass.

Newton’s Second Law

Vocabulary

Which shopping cart will have more acceleration if the same force is applied to both carts?

small

mass

large

mass

same size force

same size force

greater acceleration smaller

acceleration

So… Increasing Mass Decreases Acceleration!

Which shopping cart will have more acceleration?

same

mass same

mass

greater acceleration smaller

acceleration

greater force

smaller force

So… Increasing Force Increases Acceleration!

An apple and a bowling ball are pushed with the same force. Which one will accelerate

more? Why?

The apple will accelerate more because it has less mass.

Calculating Force

F = maF = force

m = mass

a = acceleration

Calculating Force Class Example

• What force is needed to accelerate a 10 kg shopping cart 3 m/s2?

F = m x a

F = 10 kg x 3 m/s2

F = 30 N

Calculating ForcePractice Problem #1

• If a 5 kg ball is accelerating 1.2 m/s2, what is the force on it?

F = 5 kg x 1.2 m/s2

F = 6 N

Calculating ForcePractice Problem #2

• A person on a scooter is accelerating 2 m/s2. If the person has a mass of 50 kg, how much force is acting on that person?

F = 50 kg x 2 m/s2

F = 100 N

Calculating Acceleration

m

Fa

What would the equation look like if I knew the force and the mass, but needed to find the acceleration?

Calculating AccelerationClass Example

• If a team pulls with a combined force of 9 000 N on an airplane with a mass of 30 000 kg, what is the acceleration of the airplane?

m

Fa

kg

Na

000,30

000,9

a = 0.3 m/s2

Calculating AccelerationPractice Problem #1

• Half the people on the team decide not to pull the airplane. The combined force of those left is 4 500 N, while the airplane’s mass is still 30 000 kg. What will be the acceleration?

m

Fa

kg

Na

000,30

500,4

a = 0.15 m/s2

Calculating AccelerationPractice Problem #2

• A girl pulls a wheeled backpack with a force of 3 N. If the back pack has a mass of 6 kg, what is its acceleration?

m

Fa

kg

Na

6

3

a = 0.5 m/s2

Calculating Mass

a

Fm

What would the equation look like if I knew the force and the acceleration, but needed to find the mass?

Calculating MassClass Example

• A model rocket is accelerating at 2 m/s2. The force on it is 1 N. What is the mass of the rocket?

a

Fm

2sm

Nm

/2

1

m = 0.5 kg

Calculating MassPractice Problem #1

• Another model rocket is accelerating at a rate of 3 m/s2 with a force of 1 N. What is the mass of the rocket?

a

Fm

2sm

Nm

/3

1

m = 0.3 kg

Calculating MassPractice Problem #2

• A boy pushes a sign with a force of 10 N, and the sign accelerates 2 m/s2. What is the mass of the sign?

a

Fm

2sm

Nm

/2

10

m = 5 kg

Thinking Question

• How can an object accelerate when it does not change speed?

It can simply change direction!

True or False?

• _____ A force can make an object change direction.

• _____ If an object only changes direction then it is not accelerating.

• _____ An object moves in the direction the force is applied.

• _____ Forces can cause acceleration.

True

True

True

False

Any force that keeps an object moving in a circle is known as _____________ force.

centripetal

Vocabulary

Where does the force point towards?

If you let go of the

string, the ball would

fly off in the direction

it was headed when

you let go. This is

called the path of

inertia.

What do the blue arrows

represent?

What do the

black

arrows

represent?

centripetal force

The path of inertia