Laws of motion and momentum

State Newton's first law of motion

An object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force

Fr=0 then a=0

State Newton's second law of motion.

(Resultant) force is (directly) proportional to the rate of change of momentum.

Even if mass is changing

State Newton's third law of motion.

When two objects interact, they exert equal and opposite forces on each other.

List the characteristics of Newton's 3rd law pair forces

*Same size (magnitude)

*Are of the same type .i.e. both gravitational or normal, tension

*Last for same time duration

*Act on different bodies

*Act in different (opposite directions)

define impulse

The product of force and the time for which this force acts on an object

Explain why it is a good idea to draw your hands backward when catching a ball

By drawing your hands backwards you increase the time over which the ball's velocity changes, which decreases the rate of change of momentum. Consequently by the force applied to your hands is reduced.

is momentum a scalar or vector quantity

Vector as it is a product of a scalar (mass) and a vector (velocity)

state the principle of conservation of momentum

In an isolated system free of all external resultant forces, the total linear momentum of the system in any one direction is conserved.

(this does not exclude the possibilities of equal but opposite newtons 3rd law pairs of internal forces acting within the system)

What is completely inelastic collision

a collisions where objects stick together afterwards, this means they move off together with same speed. As much Ek is lost as possible.

What is inelastic collision

After the collision the two objects move separately and kinetic energy is lost. Most collisions are of this type and energy is lost to heat/sound and deformation of the object

What is elastic collision

Energy is tranferred between particles. The kinetic energy is conserved in the collision

what is superelastic or explosive

some form of potential energy e.g. chemical/elastic is converted to kinetic energy. The kinetic energy is larger after the collision than before.