Monday 10-15

Finish School Buses

Intro to momentum

Today

• Seatbelt paper – (Rubric handed out on Tuesday)

• Pages in yellow workbook to be completed

• Momentum– In terms of collisions– In terms of games– In terms of people

Yellow Book pages

• 2 and 3• 14• 15-22 all parts (might need to go back and

complete• 23-25 (only predictions and observations)• 27 only the scroll• 29(entire page), 30 (only chart)• 35-37 questions• 45 (entire page)

Homework

• Practice Problems p 363 (1,2)

• Problems on page 366 (1 through 6)

• 2nd law problems on pg 367 (1-3)

Would you support a law that requires all school buses to have

seat-belts?

RubricSeat belt paper (50 points) Friday

• Up to nine points each for:– At least 3 worthwhile reasons for seatbelts– At least 3 worthwhile reasons against belts– Connection between each law to seatbelts

• Up to six points each for:– Clear statement of position on seatbelts– How well the project written– Condition of project

• Up to 4 points for:– references from outside articles or other sources

Which would you rather get hit by?

• 1 bowling ball? • 1 marble ?

Momentum

• A quantity of motion

• Found by multiplying the mass of an object by its velocity

• Momentum = mass x velocity

Units

• Momentum = kg m/s

• Not the same as Forces (N = kg m/s2)

• Momentum is not a force

Momentum equation

P = m v

P

M V

2nd law and velocity equation can also be drawn in a similar fashion

Fnet = m a D = v t

M A t

If the object moves, and has mass , it has momentum

Objects gain and lose momentum due to forces being applied

To catch a tennis ball

• Your hand must apply force to the ball to make it stop moving

The change on momentum

• Related to the change in velocity

• Mass is usually kept constant

• Related to the amount of force applied

• Related to the time is takes to achieve the change

To make something stop (Change of momentum constant)Apply a lot of force in a short period of time

or

Apply a small force over a longer time

The purpose of most safety features in a car is to lengthen the

time of the accident• Air bags

Seat belts

Padding on dashboard, seats and steering wheel

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

Any other means to protect the passengers during a collision?

Other examples of change in momentum

• Catching a Foul Ball • Being hit by a foul ball

Momentum is conserved

• Conserved means that the momentum can be transferred from one object to another, but not lost to the system

Newton’s Cradle