Momentum and Conservation of MomentumLesson

MOMENTUM

Learning Goal

I can define momentum and conservation of momentum.

Today:

Get your Unit 1B Guide and take any notes that you
may need – look for Momentum/Conservation of
Momentum

The sports announcer says,


"Going into the all-star break, the New York Mets have the momentum."

The headlines declare...

“Boston Celtics Gaining Momentum."

The coach pumps up his team in a time out huddle, saying "You have the momentum; the critical need is that you use that momentum and bury them in this third quarter."

Momentum is a commonly used term in sports.

A team that has the momentum is on the move and is going to take some effort to stop.

A team that has a lot of momentum is really on the move and is going to be hard to stop.

Momentum is a physics term!

Momentum is the QUANTITY of motion that an object has.

A sports team that is on the move has the momentum.

If an object is in motion (on the move) then it has momentum.

•Momentum can be defined as
"mass in motion."

All objects have mass; so if an object is moving, then it has momentum - it has its mass in motion.

Multiple Choice

Momentum is the measurement of _____ in motion.

• Mass

• Work

• Energy

The amount of momentum that an object has is dependent upon two variables:

1. how much stuff is moving and (mass)

2. how fast the stuff is moving. (velocity)

SO…momentum depends upon two things: mass and velocity.

Multiple Choice

Because momentum is a vector measurement, it has both a magnitude and a _______.

• Direction

• Velocity

• Speed

In terms of an equation, the momentum of an object is equal to the mass of the object times the velocity of the object.

Multiple Choice

Finish the formula: Momentum = Mass * _________

• Velocity

• Acceleration

• Power

Multiple Choice

What letter is typically used to represent momentum in physic equations?

• m

• v

• p

The standard metric unit of momentum is

kg m/s.

Multiple Choice

Which of the following is a unit of measurement for momentum?

• N

• N m/s

• kg m/s

Momentum is a Vector Quantity and your math needs to reflect that.

A vector quantity is a quantity described by:

1. magnitude (which we call "amount")

2. direction.

To fully describe the momentum of a 5-kg bowling ball moving westward at 2 m/s, you must include information about both the magnitude and the direction of the bowling ball.

The momentum of that bowling ball is mass x velocity

5 kg x 2.5 m/s westward which mathmatically results in


12.5 kg m/s westward

Multiple Choice

Determine the momentum of a 60-kg halfback moving eastward at 9 m/s.

• 540 kg m/s

• 540 kg m/s eastward

• 6.7 kg m/s eastward

Multiple Choice

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

• 20,000 kg m/s

• 20,000 kg m/s northward

• 50 kg m/s northward

Multiple Choice

Determine the momentum of a 40-kg freshman moving southward at 2 m/s.

• 80 kg m/s

• 80 kg m/s southward

• 20 kg m/s southward

Multiple Choice

A car possesses 20 000 units of momentum.

What would be the car's new momentum if its velocity was doubled.

• the momentum would double

• the momentum wouldn't change

• the momentum would quadruple

Multiple Choice

A car possesses 20 000 units of momentum.

What would be the car's new momentum if its velocity was doubled AND its mass was doubled.

• the momentum would double

• the momentum wouldn't change

• the momentum would quadruple

Multiple Choice

If a 70kg man and a 40k boy are both running at the same velocity, who has more momentum?

• The boy

• The man

• They both have the same momentum

Multiple Choice

What is the momentum of a 3 kg ball moving at the velocity of 5 m/s east?

• 5 kg m/s west

• 15 kg m/s east

• 0 kg m/s

Multiple Choice

If a lion and a house cat are in a race, running the same speed, which one has more momentum?

• The lion

• The house cat

​

​

The more momentum an object has, the harder it is to stop the object or change its direction.

Multiple Choice

If two vehicles have the same mass and the drivers hit the brakes at the same time, will the fast-moving or slow-moving car be harder to stop?

• A fast-moving car

• A slow-moving car

​

The fast-moving car has a greater velocity and thus more momentum than the slow-moving car of the same mass. So, a fast-moving car is harder to stop than a slow-moving car.

Conservation of Momentum

​Momentum, Newton's Third Law and Collisions...

​Since action and reaction forces don't cancel each other out, they can cause motion in the objects involved.

Momentum, a measure of how hard it is to stop an object.

When two objects collide, each object's momentum matters in the collision.

The Law of Conservation of Momentum

​

States that any time objects collide, the total amount of momentum stays the same.

When a moving object hits another object, some or all of the momentum of the first object is transferred to the object that is hit. If only some of the momentum is transferred, the rest of the momentum stays with the first object.

The Law of Conservation of Momentum

• This law is true for any collision if no forces act on the colliding objects.

• It applies whether the objects stick together or bounce off each other after they collide.

Example of the Law of Conservation of Momentum

A white cue ball hits a red billiard ball so that the billiard ball starts moving and the cue ball stops. The cue ball had a certain amount of momentum before the collision. During the collision, all of the cue ball's momentum was transferred to the red billiard ball. After the collision, the billiard ball moved away with the same amount of momentum the cue ball had.

​As shown in the figure, the momentum before a collision is equal to the momentum after the collision.

Objects Sticking Together

​Sometimes, objects stick together after a collision. After two objects stick together, they move as one object. The mass of the combined objects is equal to the masses of the two objects added together. In a head-on collision, the combined objects move in the direction of the object that had the greater momentum prior to the collision. Together, the objects have a velocity that differs from the velocity of either object before the collision because momentum is conserved and depends on mass and velocity. When mass changes, velocity must change too.

​Objects Sticking Together

​​Sometimes, objects stick together after a collision. After two objects stick together, they move as one object. The mass of the combined objects is equal to the masses of the two objects added together. In a head-on collision, the combined objects move in the direction of the object that had the greater momentum prior to the collision. Together, the objects have a velocity that differs from the velocity of either object before the collision because momentum is conserved and depends on mass and velocity. When mass changes, velocity must change too.

​Objects Bouncing Off Each Other

In some collisions, the objects bounce off each other. During such collisions, momentum is usually transferred from one object to another object. The transfer of momentum causes the objects to move in different directions at different speeds. However, the total momentum of all the objects will remain the same before and after the collision.

​

​Examples of such collisions:

• ​bowling ball and bowling pins

• ​billiard balls

• ​bumper cars

​EXAMPLES OF CONSERVATION OF MOMENTUM

Conservation of Momentum and Newton's Third Law

• Newton's third law of motion can explain conservation of momentum.

• ​In the billiard ball example, the cue ball hit the billiard ball with a certain amount of force. This was the action force. The reaction force was the equal but opposite force exerted by the billiard ball on the cue ball.

• The action force made the billiard balls start moving, and the reaction force made the cue ball stop moving.

• Because the action and reaction forces are equal and opposite, momentum is neither gained nor lost.

Multiple Choice

The momentum of an object depends upon the object's ___________&_____________.  

• mass and speed
• mass and veloctiy
• mass and energy

Multiple Choice

The total momentum before a collision is _________ the total momentum after a collision.

• equal to 
• more than
• It depends on the type of collision

Multiple Choice

Momentum is a ____________________ quantity

• science
• vector
• energy

Multiple Choice

Which of the following has the greatest momentum?

• a scurrying cockroach

• a parked semi-truck

• more information is needed

Multiple Choice

Why does a semi truck have more momentum than a car if they are both traveling at 60kph?

• Truck is more massive

• Car is moving faster

• Car is more massive

Multiple Choice

If a momentum car is moving at 2 kg m/s and crashes into a stationary momentum car, how much momentum would transfer over to the stationary car?

• all of the momentum

• a little bit of the momentum

• zero momentum

Multiple Choice

Which would have more momentum between a train moving at 0 kph and a bug flying at 0.5 kph?

• Bug

• Train

• They are the same

Multiple Choice

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

• 20,000 N

• 20,000 Kg * m/s

• 20,000 kg * m/s north

Multiple Choice

Which has more momentum: a car stopped at a red light or a bike moving at 15 mph?

• car
• bike
• they are equal

Multiple Choice

In any collision (crash) the ______ is ALWAYS constant

• total momentum

• total Velocity

• Energy