1) Go over tests 2) Science and math in the USScience and math in the US

1) Go over tests

2) Science and math in the US

DO NOW:

1) I will hand back Black History Month reflections2) You will write a definition for “momentum” based on your present knowledge3) We will watch an X-Men clip!

Juggernaut from X-Men 3: The Last

Stand

Chapter 6: Momentum and CollisionsSection 1: Momentum and Impulse

Essential Questions:1) Why must trucks start braking sooner than cars? (according to the momentum-impulse theorem instead of the work-kinetic energy theorem)2) Why do firemen use a mattress to save people jumping from a height?

Notes: Momentum

~ definition: the product of an object’s mass and velocity~ symbol: p~ SI unit: kg(m/s)~ equation: p = mv~ a vector (because velocity is a vector)

Notes: Impulse

~ definition: the change in momentum~ symbol: ∆p~ SI unit: kg(m/s) or N(s)~ equation: ∆p = F∆t~ equation comes from…

F = ma → F = m∆v/∆t → F = ∆p/∆t

Notes: Momentum-Impulse Theorem

~ ∆p = F∆t = mvf – mvi ~ the greater the momentum of an object, the greater the time required to stop it (when force is constant) ∆p↑ = F ∆t↑~ the greater the time interval to stop an object, the lesser the impact force (when momentum is constant) ∆p = F ↓ ∆t↑

Homework

Page 204 #1,4Page 201 #1,3

Use the Sample Problems on the same pages if you

need help

DO NOW:1) I will check homework2) You will do #1 on pg 199AGENDA:1) Go over page 1992) Review impulse3) Go over homework4) Answer the first essential question


Essential Question:1) According to the momentum-impulse theorem why must trucks start braking sooner than cars?

DO NOW:

Finish challenging problem from last class

OR

1)What is the relationship between mass and stopping time? 2)What is the relationship between speed and stopping time? 3)What is the relationship between momentum and stopping time?


Essential Question:2) Why do firemen use a mattress to save people jumping from a height?

Homework

Bring in materials from home for your

“Save the Egg!” project

DO NOW: help others if you solved this problem

During last year’s NASCAR Sprint Cup, two racecars passed the finish line at the exact same time and they were both traveling an average speed of 202 mph (1 mi = 1,609 m). As they crossed the finish line, they both started braking with a force of 33,000 N because they wanted to check the replay video to determine who won. The mass of car #1 was 1.25 times greater than the mass of car #2. How long did it take each car to stop if the mass of car #2 was 704 kg? What conclusion can you make about the relationship between mass and stopping time?

Review of the Project:

Pretend that we are an engineering firm and have been asked to recreate saving devices for firefighters. Your job is to design and build a structure that will save somebody (an egg) falling from a high building (the school lobby).

You must work within these perimeters:1)Use at least three separate materials2)The structure must be set up prior to testing it (ie: you must be able to transport your structure from my room to the lobby)3)The structure must require some construction (ie: you cannot just throw a blanket and cotton balls into a box)

Physics Concept: The greater the time over which a collision

occurs, the smaller the force of impact. Thus,

to minimize the force on an object, the time must

be increased.

Fans of boxing frequently observe this same principle of minimizing the effect of a force by extending the time of collision. When a boxer recognizes that he will be hit in the head by his opponent, the boxer often relaxes his

neck and allows his head to move backwards upon impact. In the boxing world, this is known as riding the punch. A boxer rides the punch in order to extend the time of impact of the glove with their head. Extending

the time results in decreasing the force and thus minimizing the effect of the force in the collision. Merely

increasing the collision time by a factor of ten would result in a tenfold decrease in the force.

Exhibit A


Two farmers were bored so they decided to race their tractors down a cornfield. It just so happens that both farmers were 90.7 kg and their John Deere tractors both had a mass of 1,751 kg. Tractor #1 had a speed of 28 mph (1 mi = 1,609 m) and tractor #2 had a speed of 32 mph just before reaching the end of the field. How long did it take each tractor to stop in time to avoid hitting the cows at the end of the field if they both applied a braking force of 8,888 N? What conclusion can you make about the relationship between speed and stopping time?

Air bags are used in automobiles because they are able to minimize the effect of the force on an object involved in a collision. Air bags

accomplish this by extending the time required to stop the momentum of the driver and passenger. When encountering a car collision, the driver and passenger tend to keep moving in accord

with Newton's first law. Their motion carries them towards a windshield that results in a large force exerted over a short time in order to stop their momentum. If instead of hitting the windshield, the driver and passenger hit an air bag, then the time duration of

the impact is increased. When hitting an object with some give such as an air bag, the time duration might be increased by a

factor of 100 thus decreasing the force by a factor of 100.

Exhibit B


Two tractor-trailers are traveling 55.0 mph (1 mi = 1,609 m) on I-95 S. Truck #1 is half the mass of truck #2 because it is not carrying any cargo. As they go around the curve near Cottman Ave, they don’t expect to see traffic at a halt because of a recent accident. To avoid creating another accident, they both slam on their brakes with a force of 25,000 N. How long will it take each truck to stop before hitting the car in front of them if the mass of truck #1 is 2,500 kg? What conclusion can you make about the relationship between momentum and stopping time?

Nylon ropes are used in the sport of rock-climbing for the same reason. Rock climbers attach themselves to the steep cliffs by means of nylon ropes. If a rock climber should lose her grip on the rock, she will begin to fall. In such a situation, her momentum will ultimately be halted by means of the rope, thus preventing a disastrous fall to the

ground below. The ropes are made of nylon or similar material because of its ability to stretch. If the rope is capable of stretching

upon being pulled taut by the falling climber's mass, then it will apply a force upon the climber over a longer time period. Extending the

time over which the climber's momentum is broken results in reducing the force exerted on the falling climber. For certain, the

rock climber can appreciate minimizing the effect of the force through the use of a longer time of impact.

Exhibit C

AGENDA:

1)TEST YOUR EGG SAVER!2)Vote for the “Save the Egg” awards3)Discuss the lab report4)Clean Up!

Homework

Work on your “Save the Egg!”

lab report


During a street race in Fast and Furious, two guys race in the middle of the night to prove their manliness. It just so happens that both guys are 100.0 kg and their cars are both 1,000.0 kg. Car #1 has an average speed of 110 mph (1 mi = 1,609 m) and car #2 has an average speed of 100.0 mph. In the middle of the race, they see a group of cop cars approaching them so they slam on their brakes with a force of 4,000.0 N. How long does it take each car to come to a stop? What conclusion can you make about the relationship between momentum and stopping time?

In racket and bat sports, hitters are often encouraged to follow-through when striking a ball. High-speed films of the collisions between bats/rackets

and balls have shown that the act of following through serves to increase the time over which a collision occurs. This increase in time must result in a change in some other variable in the impulse-momentum change theorem.

Surprisingly, the variable that is dependent upon the time in such a situation is not the force. The force in hitting is dependent upon how hard

the hitter swings the bat or racket, not the time of impact. Instead, the follow-through increases the time of collision and subsequently contributes

to an increase in the velocity change of the ball. By following through, a hitter can hit the ball in such a way that it leaves the bat or racket with

more velocity (i.e., the ball is moving faster). In tennis, baseball, racket ball, etc., giving the ball a high velocity often leads to greater success.

Exhibit D

SAVETHE

EGG AWARDS

Documents

1) Go over tests 2) Science and math in the USScience and math in the US