# Physics Unit 4 The Newtonian World

- Created by: Sam Burley
- Created on: 17-06-13 20:07

**Newton’s Laws of Motion**

**Newton’s First Law**

· An object either remains at rest or keeps travelling at constant velocity provided no resultant force acts.

**Newton’s Second Law**

· The net force acting on an object is equal to the rate of change of the linear momentum of an object. (F=ma is just a special case where m is constant)

**Linear Momentum (****)** = mass of an object (m) x velocity (v)

**Net Force** on a body is the rate of change of momentum

(N or kgms^{-2}) - Net Force

- Change in Momentum

- Change in Time

**Newton’s Third Law**

· When two objects interact, the forces they exert on each other are equal in magnitude and opposite in direction.

**Impulse (Ns or kgms ^{-1})** = force x change in time =

**Change in Momentum**

In a force against time graph, the area underneath in the impulse

**Collisions**

**Principle of Conservation of Momentum**

· The total momentum before a collision = the momentum after a collision, provided no external forces act

**Elastic and Inelastic Collisions**

· In an elastic collision, the total *kinetic energy* of the system *remains constant.* Momentum and total energy are conserved.

· In an inelastic collision, the total *kinetic energy* in *not conserved*. Some of the KE is transformed into heat, sound, etc. Momentum and total energy is conserved.

· A total inelastic collision is when the two bodies stick together and they move off with the same velocity

**Circular Motion**

**Period (T)** is the time it takes for an object to make a complete orbit around its circular path.

**Circumference of a Circle** is radians

The **Angular Displacement** of a body is the angle in radians through which a point has been rotated.

s - Arc length

r - Radius

**One Radian** is when the Arc Length is equal to the radius

**Conversions**

Degrees --> Radians

Radians --> Degrees

**Tangential Velocity**

t is for time

**Angular Velocity**

· Is the rate at which the object’s angular displacement changes (the rate at which it is going around the circle)

** **

**Centripetal**

Definition – Moving or trending towards a centre.

**Centripetal Acceleration (a)**

An object moving along a circular path has a changing velocity, even if its speed is constant. It is being accelerated towards the centre of the circle.

**Centripetal Force**

A force that acts on a body moving in a circular path and is directed toward the centre around which the body is moving

Using the equation we get:

**Gravitational Fields**

**Newton’s Law of Gravitation**

· This law states that any two bodies attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them

**Gravitational Force**

F - The force due to the gravitational attraction between the two objects (N)

G – The Gravitational Constant

M – Mass of the…

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