P2 Topic 4 by Lee Grang

CONSERVATION of ENERGY

2015-02-04 11:32:16 UTC

PRINCIPLES:

ENERGY can never be CREATED nor DESTROYED - only ever TRANSFEREED from one form to another.

Energy is only USEFUL when TRANSFERRED from one form to another.

P2 TOPIC 4 ICD

lg1313003 — 2015-02-04 11:33:36 UTC

CALCULATING THE SPEED OF FALLING OBJECTS

2015-02-04 11:35:37 UTC

Gravitational potential energy is energy due to height.

When something falls its Gravitational Potential Energy (GPE) is CONVERTED into Kinetic Energy. (Principle of conservation of energy).

So the further something falls the faster it goes.

KINETIC ENERGY GAINED = GRAVITATIONAL POTENTIAL ENERGY LOST

However some of the G.P.E will be spread out and lost due to air resistance which means energy is lost through heat.

CAR SAFETY

2015-02-04 11:39:30 UTC

•The purpose of a seatbelt is to prevent the passenger from flying forward when the car
stops abruptly during a crash/collision

•If you aren’t wearing a seatbelt and you are in a car crash, you are twice as
likely to die than you are if you were wearing one.

•Drivers between the ages of 17-34 are the most common age group to not wear seatbelts.
They are also the age group with the highest accident rate.

•Around 40,000 people die every year from car accidents. It is thought that half of
these deaths could be prevented if the drivers/passengers had been wearing
seatbelts.

ENERGY TRANSFERS and ENERGY LOSS

2015-02-04 11:42:08 UTC

Every time energy is TRANSFERRED from one form to another.

Some energy is lost to the surroundings - often as HEAT and sometimes as sound.

E.g. chemical energy in a car would ideally all transfer to kinetic energy , but the car warms up and makes noise, so energy is lost through heat and sound.

Heat energy is transferred to cooler surrounding, which then become warmer. As the heat is transferred to cooler surroundings, the energy becomes LESS CONCENTRATED - it DISSIPATES.

According to the PRINCIPLE of CONSERVATION of ENERGY, the total amount of energy stays the same. So the energy is still there, but it can't be easily used or collected back in again.

KINETIC AND POTENTIAL ENERGY

2015-02-04 11:42:46 UTC

Kinetic energy is energy of movement

Kinetic energy = 1/2 x mass x velocity squared

The kinetic energy of something depends both on mass and velocity. The more it weighs and the faster its going, the bigger its kinetic energy will be.

Stopping Distances

2015-02-04 11:42:52 UTC

Stopping Distance = Thinking Distance + Braking Distance

Thinking distance

It takes time for a driver to react to a situation and start to apply the brakes.

The car carries on moving during this reaction time.

The thinking distance is the distance travelled in this reaction time.

The thinking distance increases if the reaction time increases.

This can happen if the driver is:

Tired
Distracted
Under the influence of alcohol or other drugs

The thinking distance also increases as the car's speed increases (as the car will travel further during the reaction time).

Braking distance

The braking distance is the distance taken to stop once the brakes are applied.

The braking distance increases if:

The car's brakes or tyres are in poor condition
The road and weather conditions are poor (icy or wet roads, for example)

GRAVITATIONAL POTENTIAL ENERGY

2015-02-04 11:44:11 UTC

GPE is energy due to height

GPE = Mass x G x Height

G = Gravitational Field Strength (N/kg) and on Earth, G is approx. 10N/kg

ENERGY CANNOT BE CREATED OR DESTROYED.

2015-02-04 11:51:31 UTC

EXTRA EXTRA information...

2015-02-04 11:53:19 UTC

http://www.eoht.info/page/Conservation+of+energy

KINETIC ENERGY GAINED = POTENTIAL ENERGY LOSED

2015-02-04 11:57:07 UTC

PE in the beginning = 50J

KE mid- way = 25 J

2015-02-04 12:06:48 UTC

WORK = POTENTIAL ENERGY

2015-02-04 12:08:31 UTC

WORK

2015-02-04 12:09:33 UTC

When a FORCE moves an OBJECT, ENERGY IS TRANSFERRED and WORK IS DONE.

1) Moving something requires 'effort' which needs a supple of energy (like fuel or food or electricity etc.).

2)It then does 'work' by moving the object - and one way or another it transfers the energy it receives ( as fuel etc.) into other forms.

3) Work done and energy transferred is equal.

WORK DONE = FORCE * DISTANCE moved in the direction of the force

Momentum

lg1313003 — 2015-02-04 12:15:41 UTC

POWER

2015-02-04 12:16:41 UTC

POWER is the rate of doing work - i.e. How much per second

Power is measured in Watts (or J/s)

2019-03-24 20:08:45 UTC

GPE is energy due to height