Warm Up 3• A student plans to design an experiment to

determine which over-the-counter antacid is most effective in neutralizing stomach acid. Construct an appropriate and testable hypothesis.

LabMomentum and

Collisions

Lab Objectives• To observe in a model system, the effects

of momentum on collisions

• TSW will be able to describe momentum changes in 2 objects before and after a collision

Groups of up to 4• Supply master

– Getting and returning supplies

• Recorder– Recording data and other writing

• Task master– Keeping the group on task

• Builder/operator– Sets up the equipment

Lab overview• Create a tube out of your sheet of paper

• Place target marbles on ruler

• Place marble(s) into tube, pull out pencil

• Record observations in data table – How many marbles make it to the end– Relative speed after collision

• Answer questions 11-16

Warm Up 4• Based on the lab observation notes below,

what might a student infer about the amounts of sodium and chlorine in the jar?

– Teacher places piece of sodium into a bottle filled with chlorine and quickly puts the cover back on.

– Sodium bursts into flames immediately, but burns only for a few seconds

– All the chlorine is used in the reaction, but a small piece of sodium is left in the jar.

Agenda• Lab Wrap-Up

• Notes

• Quiz – Momentum and Impulse

Lab follow up• Was there a relationship between the

number of balls hitting the target and the number of balls leaving the target?

• Was there a difference in speed between small marbles and big marbles as targets?

Lab follow up• What can you say about the amount of

momentum right before and right after the collision?

Conservation of Momentum• Similar to Conservation of Energy, the

amount of momentum at the beginning is the same as at the end.

• Another way to describe Action-Reaction Pairs

• p0 = pf

Types of collisions• Elastic Collision

– No loss of kinetic energy to friction or heat– No deformation– Perfect transfer of momentum

• Momentum before = Momentum after

• Examples: Billiard balls, air hockey

Types of collisions• Inelastic Collision

– Deformations occur– Kinetic energy is “lost” to friction and heat

• Momentum before = Momentum after

• Examples: Hitting a golf ball with a driver

Types of collisions• Perfect Inelastic Collision

– Two objects “join” and move together after collision

– Kinetic energy is “lost” to friction and heat

• Momentum before = Momentum after– Remember to add the masses!

• Examples: Catching objects

• Quiz

Warm Up 5• A student is boiling water as part of an

investigation to observe changes in the state of matter. List 3 safety precautions the student should take during this part of the investigation.

Momentum and the Laws of Motion

• Can you have impulse without a net force?– Compare the definition of impulse with

acceleration.– Can an object move or change direction

without a net force?

• Restatement of Newton’s 1st Law of Motion:

• A net impulse is needed to change the momentum of an object.

Conservation of Momentum• Momenta are vectors

– Direction matters

• Net momentum is conserved before and after

• You are shooting the cue ball at the 8-ball. After you hit the cue ball, it is traveling with a momentum of 8.0 kgm/s. The cue ball hits the 8-ball in an elastic collision. The 8-ball rolls away and the cue ball stops.– What is the momentum of the 8-ball?– What is the net momentum before the impact?– What is the net momentum after the impact?

Bouncing• Which has the greatest change in

momentum?

A B C

Bouncing• Bouncing an object straight back produces

the largest change in momentum

Initial = +10 kgm/s

Final =

Impulse = pf – p0

Impulse = – 10 kgm/s

Impulse = kgm/s!

Turbines use this to increase efficiency

http://www.greenenergyact.com/language/en-US/Solutions/Hydro.aspx

• Gizmo: Air Track