Momentum, Conservation of Momentum

Momentum, Conservation of Momentum

Momentum + Calculating Momentum

Momentum is a vector measurement.  (Vector: Direction + speed/measurement).

It is in the same direction as velocity.

Scientists calculate momentum by multiplying the mass of the object by the velocity of the object. 

Momentum indicates how hard it would be to stop the object. 

If you were running, you might have a mass of 50 kilograms and velocity of 10 meters per second west.

Momentum calculation: mass in kilograms x velocity in meters/second

Momentum (p)=    __________________kg-m/s west

Newton's 1st law and Momentum

Remember Newton's First Law? It said that any object moving will continue moving unless it is interfered with. That idea applies to momentum as well. The momentum of an object will never change if it is left alone. If the 'm' (mass) value and the 'v' (velocity) value remain the same, the momentum value will be constant. The momentum of an object, or set of objects (system), remains the same if it is left alone. Within such a system, momentum is said to be conserved

Here's the momentum idea in simpler terms. When you

throw a ball at someone and it hits him hard, it hurts

because it was difficult to stop (had momentum).Think

about it. If you throw a small ball and a large ball at the

same speeds, the large ball will hit a person with a greater

momentum, be harder to stop, and hurt more. When the

mass is greater (at the same speeds), the momentum is

greater.

Multiple Choice

A real car moving at 10 km/h has more momentum than a toy car moving at the same rate because ______.

• its mass is greater

• its mass is less

• it moves faster

• of friction

Multiple Choice

In any collision (crash) the ______ is ALWAYS constant

• Total Momentum
• total speed
• total Velocity
• Energy

Multiple Choice

The momentum of an object depends upon the object's ___________&_____________.  

• size and shape
• mass and speed
• mass and veloctiy
• mass and energy

Conservation of momentum

We already told you that the momentum of

an isolated object (or system of objects)

is conserved. If the net force acting on an

object is zero, then the linear momentum is

constant.

Multiple Choice

According to Newton's Laws, for every action there is an ....

• equal and opposite reaction.

• equal and parallel reaction.

• unequal and opposite reaction.

• unequal and unrelated reaction.

Multiple Choice

The recoil speed of a rifle is much less than the exit velocity of a bullet because...

• the rifle experiences a smaller force
• the rifle experiences a smaller change in momentum
• the rifle has a much greater mass
• the rifle does not obey the laws of physics

Multiple Choice

In any collision (crash) the ______ is ALWAYS constant

• Total Momentum
• total speed
• total Velocity
• Energy

Elastic & Inelastic collisions

Elastic- both objects return perfectly to their shape and retain their momentum.

Inelastic- objects permanently change shape and momentum from the system is lost to the surrounding environment (usually as heat, light, or sound).

Elastic collision

In an elastic collision (such as a

super ball hitting and rebounding from the

ground), no kinetic energy is lost. All of that

energy is still in the object, so we say that

energy was conserved. 

Inelastic collision

What about an inelastic collision? In

an inelastic collision, some of the energy will be lost to heat or sound or light or some other energy. The thing to remember is that the total energy didn't change, but some of it escaped into the air, ground, etc. Try throwing a piece of clay on the ground. When the clay slams into the ground, some of the kinetic energy of the clay was lost as heat and sound to the ground and air, and some of the heat remains in the clay. Since the velocity became zero, so did the momentum. The energy is still around, but divided up in different places.