DAY 29 LETS GO!

TODAY AT A GLANCE: 1) Center of Mass 2) The different types of collisions 3) 2-D collisions

QUIZ THIS WEEK

A DAY: Fri

B DAY: Thurs

FIRST OF ALL

Lab in my hands next time…

5 minutes for last minute discussions

SECOND OF ALL…

You do a problem for me.

THE NEW IDEA…

Boys center of mass vs. Girls

Boys: higher (vertically) center of mass compared to girls. Reason…

So that point is also where the forces on it balance out OR carry only the external forces

Bird example…

CENTER OF MASS

The center of mass of a SYSTEM obeys Newtons 2nd Law

This means that the Center of mass also obeys the conservation of momentum.

LETS SEE SOME EXAMPLES

Of the center of mass obeying these

CENTER OF MASS

Example: If you consider the Sun and an orbiting probe that is close to it, where is the center of mass of the system?

A) In space exactly between the Sun and probe

B) In space very close to the Sun C) At the center of the Sun D) Near the center of the sun, but not in

space

ANOTHER EXAMPLE

A toy rocket is launched, and is on track to land 30m away. It breaks up however into 2 pieces . One lands 35 meters away. What can you determine about the other?

It will land less than 30m from the start. If it is heavier than the 1st piece, it will land

between 25 and 30m. The heavier, the more towards 30.

If lighter than the 2nd, it will land less than 25m.

TWO TYPES OF COLLISIONS:

ELASTIC:A situation where both momentum

AND kinetic energy ( ½mv2 ) is conserved

So the system momentum AND kinetic energy before and after is the same.

If there is a change in kinetic energy, then there are forces occurring in the collision to make it non elastic

TWO TYPES OF COLLISIONS:

ELASTIC:A situation where both momentum

AND kinetic energy ( ½mv2 ) is conserved

So the system momentum AND kinetic energy before and after is the same.

If there is a change in kinetic energy, then there are forces occurring in the collision to make it non elastic (INELASTIC)

QUESTION FOR YOU

If an object is moving and hits another and they link together, can this be elastic?

EXAMPLE

Two carts of equal mass go towards each other at 20m/s. After colliding, they hit and go the opposite way at 20m/s.

Is this elastic?

M2 is at rest, get hits by larger M1. Which angle is bigger of the balls after?

EQUATIONS