Collisions in One Dimension

Momentum is conserved in an WHAT system

ISOLATED system

Collisions in one dimension are also called WHAT. They involve objects moving in a WHAT line

Collisions in one dimension are also called LINEAR COLLISIONS. They involve objects moving in a STRAIGHT line

ie) In the SAME or in OPPOSITE directions

What does it mean fir momentum to be conserved ?

In an isolated system the SUM of the initial momentum equals the SUM of the final momentum

Conservation of momentum can be written mathematically like WHAT

Σpi = Σpf

Where Σ is the greek symbol “sigma” and means “ the sum of”. This is a conservation law, just like conservation of energy

What is a system

Two or more objects

External force = WHAT

A force that comes from OUTSIDE the system like gravity, normal force, friction or APPLIED force → important

Internal force = WHAT

A force taht comes from INSIDE the system. Contact between the two objects in a system are INTERNAL → can be ignored

2 factors of an isolated system

1. Momentum is conserved

2. Kinetic energy can be lost

A system is isolated, and therefore momentum is conserved when WHAT

1. NO external forces act on the system

2. External forces so act on a system but are BALANCED

So external forced cancel

yes → system is isolated → momentum is conserved

No → system is not isolated → system gains or loses momentum

An isolated system is the conservation of WHAT

momentum

When momentum is conserved WHAT will occur

Objects will have EQUAL but OPPOSITE directions

What makes up an isolated system

1. No external forces

2. Or external forces are balanced

Are explosions isolated or not

Explosions are isolated

In an isolated system, momentum is always WHAT. However, kinetic energy may or may not be WHAT

In an isolated system, momentum is always CONSERVEDD. However, kinetic energy may or may not be CONSERVED

What is an elastic collisions

Total KINETIC energy of the system is CONSERVED

What is an inelastic collisions

Total KINETIC energy of the system is NOT CONSERVED

The words elastic /inelastic tell us about the WHAT, NOT about the WHAT. It may help to remember that WHAT and WHAT both start with E

The words elastic /inelastic tell us about the KINETIC ENERGY, NOT about the MOMENTUM. It may help to remember that ENERGY and ELASTIC both start with E

In an inelastic collisions, some of the systems total kinetic energy can be lost by

• The objects crumpling/deforming

• The objects sticking together (if this happens its called a completely inelastic collision)

• The crash making a SOUND

• The crash making HEAT

All of these results in the collision losing kinetic energy but not necessarily losing MOMENTUM

In both elastic and inelastic collisions momentum is conserved as long as the system is WHAT

Isolated

Kinetic energy conserved (elastic collision)

Momentum conserved (isolated system)

• No net external forces act on the system and nothing causes the system to gain or lose kinetic energy

Kinetic energy conserved (inelastic collision)

Momentum not conserved (system is not isolated)

• This is impossible. No collision/explosions of this type exist

• If kinetic energy is conserved, momentum is automatically conserved too

• Note momentum can be conserved without kinetic energy also being conserved

Kinetic energy NOT conserved (elastic collision)

Momentum conserved (isolated system)

• Most collisions are in this category

• These are collisions where there are no unbalanced external forces (such as friction), BUT kinetic energy is still lost (ex: collision making sound)

• examples include car crash on. a frictionless surface or a firework exploding

Kinetic energy NOT conserved (inelastic collision)

Momentum not conserved (system is not isolated)

• These are collisions where there are unbalanced external forces affecting the system. Also, something causes the system to gain or lose kinetic energy

• An example would be a car crash where friction is large

If you are asked to calculate a missing speed, velocity or mass you must assume an WHAT and then use the physics principal WHAT to calculate the missing quantity. Do NOT use WHAT

If you are asked to calculate a missing speed, velocity or mass you must assume an ISOLATED SYSTEM and then use the physics principal CONSERVATION OF MOMENTUM to calculate the missing quantity. Do NOT use CONSERVATION OF ENERGY

If you are given all of the masses and velocities, then you can check if the system is isolated or not by WHAT

Σpi = Σpf