# Lecture 2

PHY1012- Lec. 2

Quantifying Motion

introducing quantities such as speed and velocity to help us better

understand motion

Speed = change in position

change in time

velocity = speed & direction objects move

Acceleration = change in velocity

change in time

velocity has km/s and direction

so acceleration also has km/s2 and direction

momentum = mass of object x velocity of object

force = push or pull

suppose there is a system if objects and he total force on the system is zero

(velocity is zero)

The total momentum of the system is the sum of the individual momentum

of each object

the total momentum of the system is a conserved quantity. It stays the

same at all time

This is called Conservation of Momentum

Q= According to the above, can we observe one ball come in mv and 2 balls

exit with ½ mv?

m= mass of one ball v = speed of incident ball

A= YES

Total initial momentum of system: mv + 0 + 0 + 0 + 0 = mv

other balls have zero momentum

because not moving

Total final momentum of system

0 + 0 + 0 + ½ mv + ½ mv = mv*

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