Physics M3C7 Newton’s Laws of motion and momentum

State Newton’s 1st Law

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

State Newton’s 3rd law

What is the rule for a N3L pair?

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

• Same type of force with the same magnitude

Define linear momentum

State the SI units of momentum

Is momentum a vector or scalar?

• The product of an object’s mass and its velocity

• $$\operatorname{kg}ms^{-1}$$

• Vector, because it is the product of a scalar and a vector

State the principle of conservation of momentum

• For a system of interacting objects, the total moment in one direction remains constant, as long as no external forces act on the object.

What happens to momentum, total energy, and total kinetic energy for elastic and inelastic collisions?

Describe an experiment to find momentum

• Use a linear air track, place objects with a known mass in motion

• Find the velocity of the object using a stopwatch and measure the distance covered

• P = mv

State Newton’s 2nd law

Give the equation

• The net force acting on an object is directly proportional to the rate of change of its momentum, and is in the same direction

• $$F=\frac{\Delta p}{\Delta t}$$

Why is F=ma a special case?

• Only applies when the mass is constant

Define impulse

Give its equation

Give its unit

• Product of force and time of the force applied

• $$I=\Delta p=F\Delta t$$

• $Ns$ or $\operatorname{kg}ms^{-1}$

How to find impulse from a F/t graph?

• Find the area under

1D and 2D collisions

• Practise them

• For 2D, resolve the momentum in each direction