﻿ SmartLearner ## Momentum and Impulse

(This section must be read in conjunction with the CAPS, p. 99–101.)

### Momentum

• Define momentum as the product of an object's mass and its velocity.
• Describe the linear momentum of an object as a vector quantity with the same direction as the velocity of the object.
• Calculate the momentum of a moving object using:
p = mv.
• Describe the vector nature of momentum and illustrate it with some simple examples.
• Draw vector diagrams to illustrate the relationship between the initial momentum, the final momentum and the change in momentum for each of the above examples.

### Newton's second law of motion in terms of momentum

• State Newton's second law of motion in terms of momentum: The resultant/net force acting on an object is equal to the rate of change of momentum of the object in the direction of the resultant/net force.
• Express Newton's second law of motion in symbols: • Calculate the change in momentum when a resultant/net force acts on an object and its velocity:
• Increases in the direction of motion, e.g.2nd stage rocket engine fires
• Decreases, e.g. brakes are applied
• Reverses its direction of motion, e.g. a soccer ball kicked back in the direction it came from

### Impulse

• Define impulse as the product of the resultant / net force acting on an object and the time the resultant/net force acts on the object.
• Deduce the impulse-momentum theorem: • Use the impulse-momentum theorem to calculate the force exerted, the time for which the force is applied and the change in momentum for a variety of situations involving the motion of an object in one dimension.
• Explain how the concept of impulse applies to safety considerations in everyday life, e.g. airbags, seatbelts and arrestor beds.

### Conservation of momentum and elastic and inelastic collisions

• Explain what is meant by a closed (an isolated) system (in Physics), i.e. a system on which the resultant / net external force is zero.
A closed (an isolated) system excludes external forces that originate outside the colliding bodies, e.g. friction.
Only internal forces, e.g. contact forces between the colliding objects, are considered.
• State the principle of conservation of linear momentum: The total linear momentum of a closed system remains constant (is conserved).
• Apply the conservation of momentum to the collision of two objects moving in one dimension (along a straight line) with the aid of an appropriate sign convention.
• Distinguish between elastic collisions and inelastic collisions by calculation.