Momentum and change in momentum 1

Question What would you rather get hit with? A bowling Ball or a steel ball bearing? 2

Which would you rather get hit by? 1 bowling ball? 1 marble ? 3

On what information does your answer depend? 4

DEFINITION OF MOMENTUM

Calculated value Momentum is a calculated or derived value from information about forces and motion Is not an intuitive value

Momentum “Pain upon impact” “Inertia in motion” Quantity of motion found by multiplying an objects mass by its velocity It is a vector value (Magnitude and Direction) 7

Units of momentum Kg m/s 8

WHAT DOES HAVE MOMENTUM?

Who has momentum? 10

Examples of momentum Anything with mass that is in motion Any object that is not moving has NO momentum

WHAT DOES NOT HAVE MOMENTUM? 12

Examples of objects without momentum Anything that has no velocity A bus that is stopped has less momentum than a flea that is moving, but more inertia 13

What has more momentum? The statue of liberty or a toddler walking at 0.5 m/s? 14

How can one change momentum? Examples of objects changing their momentum 15

DETERMINATION OF AN OBJECTS MOMENTUM VALUE

Equation of momentum P = m v 17

Momentum equation P = m v P M V 18

Car Crashes Why do some people survive and others do not? 19

Eggs and momentum

“Impulse” CHANGE IN MOMENTUM

More examples of change in momentum 22

Impulse The measure of a change in momentum Any object that changes its mass or velocity over time changes its momentum Any change in momentum requires a net force Any application of a net force, results in a change of momentum of the object 23

Examples of net force changing momentum Hockey stick on a puck Wall on a car Bat on a softball 24

WHAT CAR HAS THE GREATER IMPULSE? The Red car that was going 45 mph stopped by the Brick Wall Or The same red car that was going 45 mph and stopped by application of Brakes WHAT CAR HAS THE GREATER IMPULSE?

Answer They have the same change in momentum The car hitting a brick wall will have more force applied over a shorter time 26

Newton’s second law and ∆p How does 2nd law relate to momentum? Acceleration = the change in velocity over change in time a = ∆v / ∆t Rewrite the 2nd law in terms of the change of momentum (This is how Newton presented the law) 27

Impulse equation mΔv = Δp = Fnet ∆t ∆v = vf - vi 28

Which parts of the equation = the impulse? Impulse = F ∆t Impulse = m ∆v Impulse = pf - pi 29

Important For a given crash, the impulse is constant regardless of how the crash occurs Impulse = mΔv 30

Time and force The length of time it takes for the crash to be complete determines the amount of force applied during the crash Seat belts Foam padding Air Bags Crumple zones 31

Time and force The longer the time allowed to exert a force, the less force is exerted 32

Again What causes a change in the momentum? 33

Answer An application of net force, producing a change in velocity (slowing down OR speeding up OR changing direction) 34

Change of momentum and Sports Baseball/ softball Golf 35

Catching a ball

Other examples In cars, air bags, seat belts, padding on dashboard, steering wheel In sports, catching a ball with a glove instead of a hand, bunting/home runs In Dance, Gymnastics: Bending at the knees

To catch a tennis ball Your hand must apply force to the ball to make it stop moving 39

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APPLICATIONS OF MOMENTUM

What determines if you live or die in an auto accident? 44

Safety features 45

Safety features in cars that protect you during a crash Seat belt Air bags Cushioned dashboard, steering weel Padded headrest Crumple zones 46

The way to survive an accident Drive a car with: Seat-belts Air bag Crumple zones Soft dashboards/padded steering wheels What benefit do these features provide? 47

What value do safety features extend? The time of the crash Impulse = Force x time 48

What value is decreased as a result of those safety features? The amount of force needed to stop the car (and you) 49

The purpose of most safety features in a car is to lengthen the time of the accident Air bags 50

Seat belts 51

Padding on dashboard, seats and steering wheel 52

Crumple zones It takes time for the parts of the car in the crumple zone to be crushed, less force applied to the passenger section 53

Any other means to protect the passengers during a collision? 54

Other examples of change in momentum Catching a Foul Ball Being hit by a foul ball 55

Again The main point of all safety devices in cars is to extend the time of the impact between human and car 56

Answer The amount of force applied is related to the length of time required to bring the driver to a stop The longer the time, the less force required 57