# Physics- key stuff

- Created by: Splash Heslin
- Created on: 11-05-15 14:52

## Distance- time graphs

- The steeper the gradient, the faster the speed.
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- Straight line= constant speed.
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- Flat horizontal= standing still
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- Curved = acceleration

## Velocity graphs

- Straight line= acceleration

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- Flat horrizontal= constant speed

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- Distance travelled = area under graph

## Force

- Units for force: N

## Momentum

**mom= m x v**

- Momentum is a vector.
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- Unit for momentum=
**kgm/s**

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Explosions:

Mom before = mom after

## Stopping Distance

Reaction time: how long it takes to see someting, process it, and react.

Thinking distance:the distance moved (in car) when you are processing something (dog in road).

Breaking distance: the distance travelled once you have hit the breaks.

stopping distance= thinking + breaking

## Factors affecting stopping distance stuff

Factors affecting reaction time:

- drugs
- tiredness
- age
- drunkness

Factors affecting breaking distance:

- condition of car
- condition of road
- massof car
- speed of car

## Hooke's Law- Extention

Extention= new length - orginal length

- force= mass x gravity
- gravity= 10
- curve on top of line graph is the elastic limit!

spring constant= Force / extention

## Terminal velocity

**Terminal velocity:**

- 0 resulutant force
- 0 acceleration
- costant speed

Faster= more air resistance

- Eventually, all energy is used up to overcome air resistance.
- =forces are balanced when object is falling.

## Energy

**Work done= force x distance moved**

Units for energy: **joules**

*Power = work done / time taken*

1 watt = 1J / 1s

* EP= m x g x h *Gravitational potential

* EK= 1/2 mv* Kinetic

## Moments

Moment- turning effect of a force (pivot)

**moment of force= force x perpendicular distance from pivot**

- Moments have a direction
- .
- Centre of mass: point where an object's mass is

.thought to act through

- wide base = more stable
- lower centre of mass = more stable

## Circular motion + pressure

**Circular motion:**

- Velocity has a
**direction**, as is changeing. If velocity changes, there must be an accelaration. Therefore, an object going at the same speed can be accelerating (in a circle) - Centripetial force: force acting towards centre of mass.
- .

**Pressure:**

**pressure= force / area**

## Lenses

**Convex/ converging: **forms a real image.

**Concave/ diverging:** forms a virtual image.

**Lense Formula: 1 + 1 = 1 u v f**

**Magnification: image height object height**

**Power of Lense: 1 focal length**

** **

## The eye

** Short sight:** light focuses too quickly. Only see close objects clearly.

correction: **diverging lense.**

** Long sight:** light focuses behind retina. Only distant objects clearly.

correction: **converging lense.**

## Electric current

If an object looses electons it becomes positive

If an object gains electrons it becomes negative.

Ion: a charged atom

Electric current: a flow of charge. Measured by an ammeter. AMPS

Battery: two or more cells connected together.

current= charge flow time taken

## Potential Difference

Potential Difference: Voltage = potential difference

A mearure of energy transferreent across a component

Meassured by volt meter. VOLTS.

**potential difference= energy transferred charge**

Resistance: ions resit the passage of electrons

Measured in : ohms

**resistance= potential difference ** Larger resistance= smallercurrent ** current**

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