# physics unit 2

- Created by: tom
- Created on: 03-04-13 22:03

**Physics Unit 2 Formulae, Definitions & Notes**

** **

The slope on a **distance-time graph** represents speed

Speed (m/s) = distance travelled (metre, m) / time taken (seconds, s)

Velocity is speed in a *given direction*

Acceleration (metre/second squared, m/s^{2)} = change in velocity (metre/second, m/s)

time taken for the change (second, s)

The slope on a **velocity-time graph** represents acceleration. The area under the line on a velocity-time graph represents distance travelled. In order to find the area of a period of constant acceleration represented by a rectangle on the graph, multiply the height by the base.

In order to find the area for a period of acceleration or deceleration, i.e, a triangle; multiply ½ the height by the base.

On a distance-time graph the slope of the line = the height of the triangle

the base of the triangle

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

The unit of force is the **Newton****, N. 1N = about 100g on Earth**

Resultant force (Newtons, N) = mass (kg) x acceleration (metres/second^{2})

**Thinking distance –** distance travelled by the vehicle in the time it takes the driver to react

**Braking distance –** the distance the vehicle travels under the braking force

**Stopping distance =** thinking distance **+** braking distance

** Weight** of an object – the force of gravity

**the object**

*on***Mass** of an object – the quantity of matter ** in** it

Gravitational field strength = N/kg. GFS at the surface of the Earth is about 10N/kg

**Weight** = mass (kg) x gravitational field strength (N/kg)

**Terminal velocity** – when an object reaches a constant velocity where the drag force on it is equal and opposite to its weight. The resultant force is zero, so acceleration is also zero. An object falling freely accelerates at about 10 m/s

**Work done (joules, J)** = force (N) x distance moved in the direction of the force (m)

The kinetic energy of a moving object depends on its mass and its speed.

Kinetic energy (J) = ½ x mass (kg) x speed^{2} (m/s^{2})

**Momentum (kg m/s)** = mass (kg) x velocity (m/s)

**Momentum** is conserved in any collision or explosion provided no external forces act on the objects that collide or explode. Momentum has **size** and **direction**, and when two objects push each other apart they move apart with ** equal** and

**momentum.**

*opposite*

The more time an impact takes, the less force exerted.

**Force (N)** = change of momentum (kg m/s)

time taken (s)

To eliminate static electricity use antistatic materials and earth metal pipes and objects.

A **battery** consists of **two or more** cells connected together.

The unit of resistance is the Ohm **Ω**…

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