PH11-Momentum&Impulse

Momentum and Impulse

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By the end of the next two classes, you should be able to do the following:

Momentum L: Momentum Basics It is expected that students will demonstrate an ability to describe and apply the concept of momentum to everyday situations.

//__ It is expected that students will: __//

L1. Use the definition of momentum to calculate the unknown variable, given any two of the following:

· Momentum · Mass · Velocity

L2. State the law of conservation of momentum for isolated, one-dimensional systems

L3. Use the law of conservation of momentum to calculate any of the following from appropriate data: · Momentum · Mass · Velocity

L4. Identify workplace applications where momentum is measured or controlled

By the end of __Friday's__ class, you should have the following done: -Worksheet to accompany this webpage -Video added to the discussion tab -Phet Lab - Momentum -Workbook questions on Momentum complete Extra: Ch 9 Textbook Practice Problems (1-10)

The BIG THREE:

1) Impulse = Change in Momentum 2) Explosions 3) Collisions (both elastic and inelastic)

Review Newton's 3 Laws of Motion:

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stop, a bowling ball or a baseball?" ||
 * [[image:http://www.stmary.ws/highschool/physics/home/notes/dynamics/momentum/geekQuestion.gif width="200" height="200" align="center"]] || "Which is tougher to

||  || <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">If the baseball had a <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">much larger velocity, it <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">would be harder to stop. ||  ||
 * [[image:http://www.stmary.ws/highschool/physics/home/notes/dynamics/momentum/bowler.gif width="200" height="200" align="center"]] || [[image:http://www.stmary.ws/highschool/physics/home/notes/dynamics/momentum/baseball_pitcher_pitching_fastball_lg_wht.gif width="214" height="179" align="right"]] ||
 * <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">It Depends ....

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">I. __<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">Momentum __<span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">- the property of a moving object has that __makes it difficult to stop__. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">Also thought of as 'mass in motion' or 'moving inertia'



Momentum = Mass x Velocity

<span style="display: block; font-family: 'arial black',gadget,sans-serif; font-size: 220%; text-align: center;">p = mv

(kg•m/s) = (kg)(m/s)

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">a) vector quantity

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">b) p has same direction as velocity <span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">c) units : kg•m/s

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">Your turn....Find a video of an object with a HUGE momentum. Estimate it's mass. Estimate its velocity. Calculate its momentum.

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">Share your findings with two other students. Choose one video from the three. Post the video link, including your momentum calculation (including knowns and unknowns!) in the discussion tab at the top of this page.

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">What has more momentum? <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">1. A 25 kg artillery shell going 600 m/s <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">2. A 900 kg Honda Civic going 50 km/hr

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">A little bit of math......

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">Relationship between force and momentum: <span style="color: #ff0007; font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">Remember <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">: 'Delta' Δ means: 'change in'

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">When a force acts on a body.....it changes its velocity and its __momentum__.

<span style="display: block; font-family: 'arial black',gadget,sans-serif; font-size: 200%; text-align: center;">p = mv (from above)

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">so ...

<span style="display: block; font-family: 'arial black',gadget,sans-serif; font-size: 200%; text-align: center;">Δp = mΔv

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">From Newton's 2nd Law:.... .

<span style="display: block; font-family: 'arial black',gadget,sans-serif; font-size: 200%; text-align: center;">F = ma <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">and a = Δv/Δt

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">so ...

<span style="display: block; font-family: 'arial black',gadget,sans-serif; font-size: 200%; text-align: center;">F = m (Δv/Δt)

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">(Cross Multiply)

<span style="display: block; font-family: 'arial black',gadget,sans-serif; font-size: 200%; text-align: center;">FΔt = mΔv <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">Since ...

<span style="display: block; font-family: 'arial black',gadget,sans-serif; font-size: 200%; text-align: center;">Δp = mΔv <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">Then we get the Impulse - Momentum Theorem...

<span style="color: #ff0000; display: block; font-family: 'arial black',gadget,sans-serif; font-size: 200%; text-align: center;">FΔt = Δp

<span style="color: #ff0000; display: block; font-family: 'arial black',gadget,sans-serif; font-size: 200%; text-align: center;">Impulse (J) = Change in Momentum (caused by a force) <span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif; font-size: 220%;">*** J = FΔt = mΔv = m(v** <span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif; font-size: 220%; vertical-align: sub;">**2** <span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif; font-size: 220%;">**- v** <span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif; font-size: 220%; vertical-align: sub;">**1** <span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif; font-size: 220%;">**) = Δp** *

<span style="color: #000000; font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">The time in the formula can be thought of as 'follow through'

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<span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">A 58 g tennis ball hits a tennis racket at 125 km/hr [W]. It rebounds at 150 km/hr [E]. The contact time was 0.085 s. Consider East as positive. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">a) Find the initial and final momentum of the ball. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">b) Find the change in momentum of the ball (this is also the IMPULSE!) <span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">c) Find the force exerted on the ball

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 200%;">Another example of 'follow through' - or the amount of time - that the stick is in contact with the puck

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<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">Check out this video

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">This diver hits the water with a velocity (call it v1) and comes to a stop under the water (v2 = 0)

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">Explain, using the Impulse - Momentum Theorem why it's better to jump into water than it is to jump onto land.

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">or....

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 200%;">why long jumpers land in sand and not on solid ground?

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<span style="font-family: 'Comic Sans MS',cursive; font-size: 200%;">And then there was another Law.......

<span style="font-family: 'Comic Sans MS',cursive; font-size: 200%;">This one has a very fitting name for our exploration today...... <span style="color: #ff0200; font-family: 'Comic Sans MS',cursive; font-size: 200%;">The Law of Conservation of Momentum <span style="font-family: 'Comic Sans MS',cursive; font-size: 200%;">............which states:

__//<span style="font-family: 'Comic Sans MS',cursive; font-size: 200%;">"The Momentum of any closed, isolated system remains constant" //__

<span style="font-family: 'Comic Sans MS',cursive; font-size: 200%;">System: Any collection of objects <span style="font-family: 'Comic Sans MS',cursive; font-size: 200%;">Closed System: Objects do not enter or leave the system <span style="font-family: 'Comic Sans MS',cursive; font-size: 200%;">Isolated: No external forces act on it

<span style="font-family: 'Comic Sans MS',cursive; font-size: 200%;">Where does this apply and Why do we care? -- Collisions and explosions.

<span style="font-family: 'Comic Sans MS',cursive; font-size: 200%;">In Mathematical terms, you just need to remember that

<span style="display: block; font-family: 'comic sans ms',cursive; font-size: 200%; text-align: center;">pbefore = pafter

<span style="font-family: 'Comic Sans MS',cursive; font-size: 160%;">Before or after what? A collision or explosion between two object we'll call a and b......

<span style="display: block; font-family: 'comic sans ms',cursive; font-size: 200%; text-align: center;">pa + pb = pa’ + pb’ <span style="font-family: 'Comic Sans MS',cursive; font-size: 200%;">or.....

<span style="display: block; font-family: 'comic sans ms',cursive; font-size: 200%; text-align: center;">mava + mbvb = mava’ + mbvb’

<span style="font-family: 'Comic Sans MS',cursive; font-size: 150%;">The prime ' indicates the velocity of the object after the collision/explosion

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 160%;">Here is an example of an explosion question:

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 160%;">Two lab carts are initially at rest. A spring pushes the two apart, causing one to move to the right at 2.0-m/s (of mass 0.75 kg), and the other to move in the opposite direction at 6.0-m/s. What is the mass of the second cart?

Now how about Elastic vs. Inelastic collisions? This one is your's to explore! Thankfully....you have this lab to complete to get there!~

LAB:

Find the applet here


 * Ch9 Textbook Solutions **[[file:Chapter 09 Solutions.doc]]

Another good momentum video

Another good momentum resource

This guy does online physics lessons. Feedback from other users (students like yourselves!) seemed to be positive, so I thought I would post it here:

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Another explosion question.....we'll have the chance to try this at the skating rink next month!

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If you are looking for that extra challenge, Physics 12 deals with the concept of momentum in 2 dimensions, which is shown here:

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Other good videos showing Momentum in action! media type="youtube" key="zS_Gk7vjmOg" height="315" width="560"

<span style="font-family: 'Comic Sans MS',cursive; font-size: 120%;">Class Notes and examples