Momentum

An objects momentum is its mass multiplied by its velocity

Momentum = mass * velocity

Kg m /s kg m/s

Mass

= 1000 kg V = 6 m / s

Momentum = 1000 *6 = 6000 kg m / s

Momentum & collisions

When two objects collide they exert an equal & opposite force on each other

The force (they apply) = change on momentum

time

Reducing the force in accidents

You can explain air bags, seat belts etc using momentum

Ie the longer the time an accident takes means momentum is changed over a longer time reducing the force

Mass = 1000 kg

Initial velocity 5 m/ s

If it stops in 2 seconds

Force = 1000 * 5

2

= 2500 N

Force = 1000 * 5

5

= 1000 N

If it stops in 5 seconds

Momentum can explain……Rockets

Momentum of gas this way = Momentum of

rocket this way

Recoil of a gun

Mass * velocity of cannon = Mass * velocity of cannon ball

The momentum is conserved, so the momentum to the left must equal momentum to the right

Momentum & collisionsCarriage A is rolling towards carriage B which is stationary. They stick together after the crash. What is the new velocity?

A

Mass 10 000 kg.

Velocity 5 m/s

B

Mass 10 000 kg.

Velocity 0 m/s

A + B

Momentum before the crash = momentum after the crash

m * v + m * v = m * v

10 000 * 5 + 10 000 * 0 = 20 000 * V

50 000 + 0 = 20 000 * V

50 000 = V = 2.5 m/s

20000

Polarization of light (Sunglasses)

Polarization of light (Sunglasses)

• Light normally travels in random planes

• Filters can “polarize” light, only light in a certain plane can get through

• Polarized sunglasses block out horizontal light (for example light that reflects off light surfaces such as the sea. Only light in the “Y plane” gets through. Reducing the strain on your eyes.

Adding waves

If they are in phase (crests line up)

=Constructive

interference

If they are out of phase (crests and troughs line up)

=

Destructive

interference

Two slit experiment

Path difference is a wholenumber of wavelengths.

Constructive interference

Bright area

Path difference is a an oddnumber of

halfwavelengths.

Destructive interference

Dark area

Laser light source