What You Should Know About
The Physics of Driving

Codman Academy Charter Public School
Physics 10A | 2004-2005
Teacher: Regan Brooks
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Impulse & Momentum
Impluse and Momentum
This picture shows what happens when you get into a accident and the airbags shoot out at you.Momentum is Inertia in motion. Momentum can be calucated as mass times velocity.
The abbreviation for momentum is "p".

A moving object can have a large momentum if it has a large mass, a high speed or both.
For example, a moving truck has more momentum. Than a car moving at the same speed because the truck has more mass. However, a fast car can have more momentum than a slow truck especially if the truck is at rest is has no momentum at all.

If the velocity of an object changes then the momentum changes. We call this impulse.
Impulse = change in momentum

To increase the momentum of an object you will need to apply a net force that is greater than zero. That way the object will acccelerate and velocity will increase.

When talking about impulse and momentum, we should also talk about impact. Impact can be broken into two parts, force of impact and time of impact.

Impulse= force of impact x time of impact
Force of impact= force of contact
Time of impact= time of contact



This picture shows a perfect car that has not been crashed
If two cars with different masses crash head to head at identical speeds, they both experience the same change in momentum. In other words they will both experience the same impluse.

When both cars crashed they will experience equal and opposite forces and they also have identical time of impact. However, because they have different masses they will experience different changes in velocity or acceleration. 

Airbags protect you from hitting your head on the dash-board if the car comes to an immediate stop. The seat belt ensures your safety when a car has to come to a quick stop. The crumple zones of a car helps  the car absorb the force of impact. This is why you need safty devices in every car. Crumple zone in cars increase the time of impact and that decreases the force of impact.
 



Impulse and Momentum Resources

This weblink gives you a better understanding of momentun and energy and how it works. It also gives you pictures and animations.
htp://sol.sci.uop.edu/~jfalward/physics17/chapter3/chapter3.html

This weblink is about momentum in the physics classroom and gives you animations.
http://www.glenbrook.k12.il.us/gbssci/phys/Class/momentum/u4l1a.html

This weblink is about the physics of roller coasters.
http://www.learner.org/exhibits/parkphysics/

This weblink contains an About.com article on momentum.
http://physics.about.com/cs/workedproblems/a/131003.htm

This weblink is about the physics of hockey (momentum and hockey).
http://www.madsci.org/posts/archives/feb2002/1014740763.Ph.r.html

This weblink has more on momentum and hockey.
http://www_hockey.tripod.com/
Impulse and Momentum Quiz
This picture shows a situation when two cars crashTo take this quiz on line and have it graded please click here.


1. True or False?
    Momentum= Mass times Velocity
 
2. The abbreviation for momentum is?
a. mph
b. VIP
c. p

3.The force of contact equals ?
a.The time of contact that something has hit?
b.The mass of contact that something has hit?
c.The force of contact that something hit?
   
4.True or false? 
Impluse equals change in momentum.

5.If a truck is at rest it has...
a. More mass
b. Less mass
c. No momentum

6.Why does a moving truck have more momentum than a car moving at the same speed ?
a. the truck has less mass
b. the truck has more mass
c. the car is on the truck

7.What does crumple zones absorb in a car?
a. The force of the car.
b. The mass of the car.
c. Force of contact.

8. What is impulse equal to?
a. Time of contact.
b. Force of contact.
c. Change in momentum.

9. Momentum is what in Motion?
a. Velocity
b. Inertia
c. Speed
d. Light 

10. How do airbags help you in a car accident?
a. They increase the force and decrease the time.
b. They reduce the force of impact by increasing the time of impact.
c. They shoot out at you with no control.
d. They kill you.


This picture shows how the crumple zone works


 



This is a picture of Sherica dropping an egg onto her platform.Experiment/ Demo

Egg Drop!

What you'll need:
For each groups of two or three students:
copier paper, 10 sheets (8 ½” by 11”)
masking tape, 1.0 meter
scissors, one pair and a egg

What to do:
You have to use the 10 sheets of paper and the 1 meter of tape to make a platform for your egg to land on.  Each group will get 2 eggs, one as a practice egg (to use before you start the big drop). For the big drop you will take your meter stick and every group will have a turn dropping their egg onto their platform. You will first start at 1 meter and then you will do 2 meters and so on until there is one group (with an unbroken egg) left.  The group with the egg that survives the last drop will be the winner.

What to notice:
You will have to look at the egg to see is it is broken, but if it has a little crack and the yolk is not coming out you can go on to the second round.

What's going on:
If the egg has broken, there was too much force because your platform did not increase the time of impact enough. If it did not break you successfully mastered the egg drop. Your platform did increase the time of impact and the force of impact was decreased!

Further Questions:
1) What would happen if you wet the paper?
2) What do you think makes the most difference, the mass of the platform or the force that the egg hits the platform at?
3) What if your platform was an air bag, would it be safe?

Credits:
Thanks to Griff Jones who put together the curriculum “Understanding Car Crashes: It's Basic Physics.”




This website was created, with their best intent, by Sherica, Tatiana, and Minnetta!


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