Forces Notes Part 2

Newton's Laws

Objectives

The students will be able to:

• Rank objects based on amount of inertia

• Rank objects based on amount of momentum.

• Given a scenario, identify and explain which law is at work.

• Find net force on an object based on a picture or diagram.

• Calculate weight of an object, given its mass.

Net Force: the combining of forces when two or more forces act on an object.

​

​F= 2 N

​F= 5 N

• Forces on an object can be balanced or unbalanced.

​Balanced Forces: forces that are equal in size and opposite in direction.

• Does not cause a change in motion because the net force on the object is 0.

​F= 4 N

​F= 4 N

Multiple Choice

Calculate the Net Force. 

• 60N, Left 
• 40N, Right 
• 0N
• 60N, Right

Multiple Choice

What kind(s) of objects have inertia?

• all objects with mass
• only objects at rest
• only objects in motion
• only objects whose motion is being changed

Law of Universal Gravitation

Law of Universal Gravitation: Any two masses exert an attractive force on each other.

Newton's 2^nd Law of Motion

Newton’s 2nd Law: A net force acting on an object causes the object to accelerate in the direction of the net force.

Newton's 2^nd Law of Motion

Newton’s 2nd Law: A net force acting on an object causes the object to accelerate in the direction of the net force.

• The greater the mass, the greater the force needed to accelerate it.

Newton's 2^nd Law of Motion

Newton’s 2nd Law: A net force acting on an object causes the object to accelerate in the direction of the net force.

• The greater the mass, the greater the force needed to accelerate it.

• The greater the net force, the greater the acceleration.

Newton's 2^nd Law of Motion

Newton’s 2nd Law: A net force acting on an object causes the object to accelerate in the direction of the net force.

• The greater the mass, the greater the force needed to accelerate it.

• The greater the net force, the greater the acceleration.

• ​The ball will accelerate in the direction of the net force the mallet applies.

Newton's 2^nd Law of Motion

Newton’s 2nd Law: A net force acting on an object causes the object to accelerate in the direction of the net force.

• The greater the mass, the greater the force needed to accelerate it.

• The greater the net force, the greater the acceleration.

• ​The ball will accelerate in the direction of the net force the mallet applies.

• The greater the force applied, the faster the ball will move.

Newton's 2^nd Law of Motion

• Can be summarized as an equation:

​F= force	m = mass	a = acceleration
​Measured in Newtons (N)	measured in kilograms (kg)	measured in m/s

​​F = m x a

Multiple Choice

What is the formula for calculating Force?

• F=m x a

• a=F÷m

• m=F x a

• F=m÷a

Multiple Choice

What is the formula for calculating acceleration?

• a=F÷m

• F=m x a

• m=F÷a

• a=F x m

Multiple Choice

What is the formula for calculating mass?

• a=F÷m

• F=m x a

• m=F÷a

• m=F x a

Multiple Choice

What does this picture represent

• Force,magnetism,acceleration

• Force, money, Apples

• Force, Mass, Acceleration

• Funny, monkeys, Arrive

Newton's 2^nd Law of Motion

• Example #1: You are pushing a friend on a sled.  You push with a force of 40N.  Your friend and the sled together have a mass of 80 kg.  Ignoring friction, what is the acceleration of your friend on the sled?

​​F = m x a

Newton's 2^nd Law of Motion

• Example #1: You are pushing a friend on a sled.  You push with a force of 40N.  Your friend and the sled together have a mass of 80 kg.  Ignoring friction, what is the acceleration of your friend on the sled?

​​F = m x a

Newton's 2^nd Law of Motion

• Example #1: You are pushing a friend on a sled.  You push with a force of 40N.  Your friend and the sled together have a mass of 80 kg.  Ignoring friction, what is the acceleration of your friend on the sled?

​​F = m x a

​F = 40 N

m = 80 kg

a = ?

Newton's 2^nd Law of Motion

• Example #1: You are pushing a friend on a sled.  You push with a force of 40N.  Your friend and the sled together have a mass of 80 kg.  Ignoring friction, what is the acceleration of your friend on the sled?

​​F = m x a

​F = 40 N

m = 80 kg

a = ?

a = F ÷ m

Newton's 2^nd Law of Motion

• Example #1: You are pushing a friend on a sled.  You push with a force of 40N.  Your friend and the sled together have a mass of 80 kg.  Ignoring friction, what is the acceleration of your friend on the sled?

​​F = m x a

​F = 40 N

m = 80 kg

a = ?

a = F ÷ m

a = 40 N ÷ 80 kg

Newton's 2^nd Law of Motion

• Example #1: You are pushing a friend on a sled.  You push with a force of 40N.  Your friend and the sled together have a mass of 80 kg.  Ignoring friction, what is the acceleration of your friend on the sled?

​​F = m x a

​F = 40 N

m = 80 kg

a = ?

a = F ÷ m

a = 40 N ÷ 80 kg

a = 0.5 m/s²

Weight: The force of gravity on an object

Weight

Weight: The force of gravity on an object

• Because it is a force, you can always calculate weight using

Weight

​F = m x a

Weight: The force of gravity on an object

• Because it is a force, you can always calculate weight using

• When finding weight, acceleration due to gravity is always used = 9.8 m/s2

Weight

​F = m x a

Newton's 2^nd Law of Motion

• Example #2: Find the weight of a suitcase that has a mass of 42 kg.

​​F = m x a

Newton's 2^nd Law of Motion

• Example #2: Find the weight of a suitcase that has a mass of 42 kg.

​​F = m x a

Newton's 2^nd Law of Motion

• Example #2: Find the weight of a suitcase that has a mass of 42 kg.

​​F = m x a

​F (weight) = ?

m = 42 kg

Newton's 2^nd Law of Motion

• Example #2: Find the weight of a suitcase that has a mass of 42 kg.

​​F = m x a

​F (weight) = ?

m = 42 kg

a = 9.8m/s²

Newton's 2^nd Law of Motion

• Example #2: Find the weight of a suitcase that has a mass of 42 kg.

​​F = m x a

​F (weight) = ?

m = 42 kg

a = 9.8m/s²

F = m x a

Newton's 2^nd Law of Motion

• Example #2: Find the weight of a suitcase that has a mass of 42 kg.

​​F = m x a

​F (weight) = ?

m = 42 kg

a = 9.8m/s²

F = m x a

F = 42 x 9.8

Newton's 2^nd Law of Motion

• Example #2: Find the weight of a suitcase that has a mass of 42 kg.

​​F = m x a

​F (weight) = ?

m = 42 kg

a = 9.8m/s²

F = m x a

F = 42 x 9.8

F (weight) = 411.6 N

Multiple Choice

Which law of motion says that you must push or pull objects harder if they have more mass?

• 1st

• 2nd

• 3rd

• 4th

Multiple Choice

How much force is needed to accelerate a 2 kg physics book to an acceleration of 6 m/s/s?

• 36 N

• 12 N

• 3 N

• 0.33 N

Multiple Choice

You pull horizontally on a 50-kg crate with a force of 500 N, and the friction force on the crate is 250 N. The acceleration of the crate is (find net force, use formula)

• zero

• 2 m/s/s

• 4 m/s/s

• 5 m/s/s

Multiple Choice

A jumbo jet cruises at a constant velocity when the force from the engines on the jet is 40000 N. How much air resistance acts on the jet?

• 80000

• 60000

• 40000 N

• 20000

Multiple Choice

What Unit do we Measure Force in?

• Newtons

• Joules

• Force

• Kilograms

Weight vs. Mass

• Mass = the amount of matter in an object.

Weight vs. Mass

• Mass = the amount of matter in an object.

• Weight = the force of gravity on an object

Weight vs. Mass

• Mass = the amount of matter in an object.

• Weight = the force of gravity on an object

  • Meaning it can change based on location!

Weight vs. Mass

• Mass = the amount of matter in an object.

• Weight = the force of gravity on an object

  • Meaning it can change based on location!

  • The further from Earth you are, the lower your weight

Weight vs. Mass

• Mass = the amount of matter in an object.

• Weight = the force of gravity on an object

  • Meaning it can change based on location!

  • The further from Earth you are, the lower your weight

    • On the moon your weight would be 1/6th what it is now.

Weight vs. Mass

• Mass = the amount of matter in an object.

• Weight = the force of gravity on an object

  • Meaning it can change based on location!

  • The further from Earth you are, the lower your weight

    • On the moon your weight would be 1/6th what it is now.

  • If you could be on another planet your weight would change based on the gravity of that planet

Weight vs. Mass

• Mass = the amount of matter in an object.

• Weight = the force of gravity on an object

  • Meaning it can change based on location!

  • The further from Earth you are, the lower your weight

    • On the moon your weight would be 1/6th what it is now.

  • If you could be on another planet your weight would change based on the gravity of that planet

    • On Jupiter your weight would be over twice as much as it is now.

Multiple Choice

Measure of acceleration due of gravity =

• 9.8 kg

• 9.8 N

• 9.8 m/s²

Multiple Choice

If there is a big mass, it would need a stronger force to accelerate it. Which law does this describe?

• 3rd law

• 1st law

• 2nd law

Multiple Choice

Measure of the amount of matter

• Mass

• Weight

Multiple Choice

Measure of the force of gravity

• Mass

• Weight

Multiple Choice

Constant no matter your location in the universe

• mass

• weight

Multiple Choice

Changes with location in the universe

• mass

• weight

Multiple Choice

Measure of the amount of force

• mass

• weight

Multiple Choice

A person would weigh less on on the Moon than on the Earth because . . .

• Moon has more mass, and therefore more gravity

• Moon has less mass, and therefore more gravity

• Moon has more mass, and therefore less gravity

• Moon has less mass and therefore less gravity

Practice Time

Newton's 3^rd Law of Motion

Newton’s 3rd Law: every action has an equal and opposite reaction.

Newton's 3^rd Law of Motion

Newton’s 3rd Law: every action has an equal and opposite reaction.

• When one object exerts a force on a second object, the second one exerts a force on the first that is equal in size and opposite in direction.

Newton's 3^rd Law of Motion

Newton’s 3rd Law: every action has an equal and opposite reaction.

• When one object exerts a force on a second object, the second one exerts a force on the first that is equal in size and opposite in direction.

  • Ex. When you jump on a trampoline, the trampoline exerts the same force on you but pushes you in the opposite direction.

Multiple Choice

This is Newton's 3rd law

• True

• False

Multiple Choice

Letting go of a balloon full of air is demonstrating Newton's ______ _______ ________ _________ because the air comes out of the back and the balloon moves forward.

• 1st law of motion

• 2nd law of motion

• 3rd law of motion

• 13th law of motion

Law of Conservation of Momentum

Momentum: (p) mass in motion.

​p = m x v

​p = momentum	​m = mass	​v -velocity
​measured in kg*m/s	​measured in kilograms (kg)	​measured in m/s

​p = m x v

Law of Conservation of Momentum

Momentum: (p) mass in motion.

​p = m x v

​p =momentum	​m = mass	​v = velocity
​measured in kg*m/s	​measured in kilograms (kg)	​measured in m/s

​p = m x v

• ​All moving objects have momentum. 

• Momentum is transferred between objects in a collision.

Law of Conservation of Momentum

In a collision, because the forces acting on the two objects are equal and opposite (Newton’s 3rd Law), the transfer of momentum must be the same.

​p = m x v

Law of Conservation of Momentum

In a collision, because the forces acting on the two objects are equal and opposite (Newton’s 3rd Law), the transfer of momentum must be the same.

​p = m x v

à Law of Conservation of Momentum: momentum is never created or destroyed in a collision, it only is transferred.

Multiple Choice

The equation for momentum is?

• momentum = force - mass

• momentum = acceleration / mass

• momentum = mass x acceleration

• momentum = mass x velocity

Multiple Choice

Like velocity, acceleration, and force, momentum is described by its direction as well as its quantity. This Means it is a _______

• scalar quantity

• vector quantity

Multiple Choice

What is true about the relationship between mass and momentum.

• The less mass an object has, the more momentum it will have.

• The more mass an object has, the less momentum it will have.

• The more mass an object has, the more momentum it will have.

• Mass has nothing to do with momentum.

Multiple Choice

Even if an object has a smaller mass, it can have a larger momentum if it has a high _______.

• velocity

• displacement

• weight

Newton's 3^rd Law of Motion

• Example #3: What is the momentum of a car with a mass of 1300 kg traveling at a speed of 28 m/s?

​​p = m x v

Newton's 3^rd Law of Motion

• Example #3: What is the momentum of a car with a mass of 1300 kg traveling at a speed of 28 m/s?

p = ?

m = 1300 kg

v = 28m/s

​​p = m x v

Newton's 3^rd Law of Motion

• Example #3: What is the momentum of a car with a mass of 1300 kg traveling at a speed of 28 m/s?

p = ?

m = 1300 kg

v = 28m/s

p = m x v

​​p = m x v

Newton's 3^rd Law of Motion

• Example #3: What is the momentum of a car with a mass of 1300 kg traveling at a speed of 28 m/s?

p = ?

m = 1300 kg

v = 28m/s

p = m x v

p = 1300 x 28

​​p = m x v

Newton's 3^rd Law of Motion

• Example #3: What is the momentum of a car with a mass of 1300 kg traveling at a speed of 28 m/s?

p = ?

m = 1300 kg

v = 28m/s

p = m x v

​​p = m x v

p = 1300 x 28

p= 36,400 kg*m/s

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

​​p = m x v

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

Due to the Law of conservation of momentum....

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

p₁= p₂

Due to the Law of conservation of momentum....

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

Due to the Law of conservation of momentum....

p₁= p₂

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

p₂ = m₂ x v₂

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

Due to the Law of conservation of momentum....

p₁= p₂

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

p₂ = m₂ x v₂

p₂ = 0.17 x 9

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

Due to the Law of conservation of momentum....

p₁= p₂

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

p₂ = m₂ x v₂

p₂ = 1.53 kg*m/s

p₂ = 0.17 x 9

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

Due to the Law of conservation of momentum....

p₁= p₂

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

p₂ = m₂ x v₂

p₂ = 1.53 kg*m/s

p₁= p₂

p₂ = 0.17 x 9

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

Due to the Law of conservation of momentum....

p₁= p₂

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

p₂ = m₂ x v₂

p₂ = 1.53 kg*m/s

p₁ = 1.53 kg*m/s

p₁= p₂

p₂ = 0.17 x 9

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

Due to the Law of conservation of momentum....

p₁= p₂

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

p₂ = m₂ x v₂

p₂ = 1.53 kg*m/s

m₁ = p₁ ÷ v₁

p₁ = 1.53 kg*m/s

p₁= p₂

p₂ = 0.17 x 9

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

Due to the Law of conservation of momentum....

p₁= p₂

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

p₂ = m₂ x v₂

p₂ = 1.53 kg*m/s

m₁ = p₁ ÷ v₁

p₁ = 1.53 kg*m/s

p₁= p₂

p₂ = 0.17 x 9

m₁ =1.53 ÷ 11

Newton's 3^rd Law of Motion

• Example #3: Ball #1 is rolling 11 m/s directly toward a 0.17 kg ball #2 at rest.  During the collision, ball #1 stops and ball #2 is launched forward at 9 m/s.  What is the mass of ball #1? (think about the Law of Conservation of Momentum)

p₁ = ?

m₁ = ?

v₁ = 11m/s

p₂ = ?

m₂ = 0.17 kg

v₂ = 9m/s

p = m x v

Due to the Law of conservation of momentum....

p₁= p₂

​​p = m x v

​m_{2 = 0.17 kg}

​m_{1 = ?}

​v_{1 = 11 m/s}

​v_{2 = 9 m/s}

p₂ = m₂ x v₂

p₂ = 1.53 kg*m/s

m₁ = p₁ ÷ v₁

p₁ = 1.53 kg*m/s

p₁= p₂

p₂ = 0.17 x 9

m₁ =1.53 ÷ 11

m₁ =0.14 kg

Multiple Choice

Determine the momentum of 1000-kg car moving southward at 20 m/s......... 

• 20000 N

• 20000 Joules

• 20000 Kg * m/s south

• 10000 kg * m/s south

Multiple Choice

A 2.5 kg ball moving at 5 m/s collides with a 2.5 kg stationary ball in a perfectly elastic collision.  What is the velocity of the second ball after the collision? 

• 5 m/s

• 2.5 m/s

• 10 m/s

• 7.5 m/s

Multiple Choice

A 9300 kg railroad car traveling at a velocity of 5 m/s strikes a second boxcar that weighs 5000 kg at rest. At what speed will the second boxcar move?

• 18.6 m/s

• 9.3 m/s

• 7.5 m/s

• 1.86 m/s

Multiple Choice

Newton's third law states that any action will have a(n) _______ and ______ reaction

• Equal and similar

• Equal and opposite

• Equal and different

• Greater and opposite