Good Morning!

• Today we will:– Do an inquiry lab– Take some notes– Do a worksheet

• Please do before the tardy bell:– Get your lab book– Get out something to write with

Marbles and Momentum

• Title the lab, “Marbles and Momentum”

• Make an entry in your table of contents – this is an “extra” lab, so it doesn’t have a chapter and section

Moving Objects HaveMoving Objects Have

So What’s Momentum ?• Momentum = mass x velocity

• This can be abbreviated to : P = mv

• So, A really slow moving truck and an extremely fast roller skate can have the same momentum.

Question :

• Under what circumstances would the roller skate and the truck have the same momentum ?

• The roller skate and truck can have the same momentum if the product of the mass and velocity of the skate equal the product of the mass and velocity of the truck.

• A 1000 kg truck moving at 0.01 m/sec has the same momentum as a 1 kg skate moving at 10 m/sec. Both have a momentum of 10 kg m/sec. ( 1000 x .01 = 1 x 10 = 10 )

1000 kg1 kg .01 m/sec10 m/sec

Momentum and Cars

• If two cars are traveling at the same speed, what is the determining factor of the momentum of each?– their masses

• The larger the mass (at the same speed), the larger the momentum

Momentum and People

• We see lots of examples of momentum (and the transfer of momentum) in football collisions

• Big Hit #1

• Big Hit #2

Keep in Mind

• For optimum momentum, you want your object to be both big AND fast

• Terry Tate

• If momentum changes, it’s because mass or velocity change.

• Most often mass doesn’t change so it’s the velocity that changes

• What is a change in velocity called?– acceleration

• Remember: mass x acceleration = force

Impulse and Momentum

The faster you push me…

• the farther I get

• Applying a force over time to an object changes the object’s momentum

• Force x change in time = Impulse

• Impulse = F t or Ft = mv

Impulse and Momentum

Ft = mv

• An object at rest has no momentum, why?– Because anything times zero is zero– (the velocity component is zero for an object at rest)

• To INCREASE MOMENTUM, apply the greatest force possible for as long as possible.

• Examples : • pulling a sling shot • drawing an arrow in a bow all the way back • hitting a golf ball or a baseball

(that’s why “follow through” is important!)

MOMENTUM

MOMENTUM

• SOME VOCABULARY :

• momentum: mass x velocity

• impulse : impact force x time

• impact : the force acting on an object (usually when it hits something)

• Decreasing Momentum • Which would it be more safe to hit in a car ?

• Knowing the physics helps us understand why hitting a soft object is better than hitting a hard one.

MOMENTUM

mv

mv

Ft

Ft

• In each case, the momentum is decreased by the same amount or impulse (force x time)

• Hitting the haystack extends the impact time (the time in which the momentum is brought to zero).

• The longer impact time reduces the force of impact and decreases the deceleration.

MOMENTUM

DECREASING MOMENTUMDECREASING MOMENTUM

• If the time of impact is increased by 100 times (say from .01 sec to 1 sec), then the force of impact is reduced by 100 times (say to something survivable).

• EXAMPLES :• padded dashboards on cars• airbags in cars• safety nets in circuses• moving your hand backward as you catch a fast-moving ball• flexing your knees when you land after jumping in the air• elastic cords for bungee jumping• using wrestling mats instead of hardwood floors.• dropping a glass dish onto a carpet instead of a sidewalk.

Decreasing Momentum on Race Tracks

• Oswego Speedway