Physics Topic 1 Energy

Kinetic energy is the energy stored in a moving objects

Stationary objects have no kinetic energy 

KE = ½ × m × v²

KE = joules

M = kg

V= m/s

Kinetic energy store depends on mass and speed of the object. The greater the mass and the faster the object is going the more energy is stored as kinetic energy 

The energy that the springs stores while being stretched is called elastic potential energy. The extension and spring are directly proportional. However, if you apply a very large force then the spring has been stretched too far it has been stretched beyond the limit of proportionality.

Elastic Potential energy = 0.5 x spring constant x extension 

Elastic potential energy = joules

Spring constant = n/m

Extension = m

Gravitational potential energy is the energy stored in an object due to its position above the Earths surface. This is due to the force of gravity acting on an object.

Gravitational potential energy = mass x gravity x height

gravitational potential energy = joules 

mass = kg

gravity = n/kg     gravity = 9.8

height = m 

1. Thermal 

2. Kinetic

3. Gravitational 

4. Elastic

5. Chemical

6. Magnetic 

7. Electrostatic

8. Nuclear 

Work is done whenever energy is transferred from one store to another

Mechanical work involves using a force to move an object

Electrical work involves a current transferring energy 

Work done = Force x Distance 

Work done = joules

Force = newtons 

Distance = meters

The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1kg of the substance by 1°C

Change in thermal energy = mass x specific heat capacity x change in temperature

specific heat capacity is measured in J / kg °C

At the start of the jump, all of the energy in the system is the store of gravitational potential energy. As the jumper falls energy is transferred from gravitational potential energy store to the kinetic energy 

When the bungee rope just starts to tighten, the kinetic energy store is now at its maximum

All of the energy has been transferred to the elastic potential energy store. When the bungee rope recoils the elastic energy stores back to kinetic.

At the top, all the energy is now in the gravitational energy. 

The jumper never returns back to the original position. This is because energy is dissipated as thermal energy. This is due to friction with air particles. It is also due to the stretching effect in the bungee rope. 

Power is the rate at which energy is transferred or the rate at which work is done.

Power = Energy Transferred ÷ Time 

Power = Work Done ÷ Time 

Power = Watts 

Energy Transferred = Joules

Work Done = Joules

Time = Seconds

1 watt = 1 joule per second 

Efficiency = useful output energy transfer ÷ total input energy transfer 

Efficiency = useful power out ÷ total power output

You can improve the efficiency of energy transfer by insulating objects, lubricating them or making them streamlined. 

At the top, the mass has the maximum store of gravitational potential energy 

As the pendulum, this energy is transferred to the kinetic energy store

The mass has maximum kinetic energy at the bottom of the swing since that is where it is moving at the fastest speed 

As the mass swings back up the kinetic energy store transfers to the gravitational potential energy

As the pendulum swings, there is friction in the fixed point

There is also friction when the pendulum passes through the air particles 

Friction causes energy to be transferred as thermal energy 

The fixed point and the air around the pendulum get warmer gradually

These stores of thermal energy are less useful. The energy has been dissipated. 

When something moves there is usually at least one frictional force acting against it

This causes energy to be dissipated

Lubricants can be used to reduce friction between the objects surfaces when they move

Lubricants are usually liquids like oil so they can flow easily between the objects and coat them.

Have thick walls that are made from a material with a low thermal conductivity.

The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across that material

The thicker the walls and the lower the thermal conductivity the slower rate of energy transfer will be 

Cavity walls made up of an inner and an outer wall with a gap in the middle. The air gap reduces the amount of energy transferred by conduction through the walls

Cavity wall insulation is when the air gap in the wall is filled with a foam so it can reduce energy transfer by convection 

Loft insulation can reduce convection currents being created in lofts

Double glazing allow having a gap between two sheets of glass prevent energy transfer by conduction

Draught excluders around doors and windows reduce energy transfer by convection 

Conduction is the process when vibrating particles transfer energy to neighbouring particles

Energy transferred to an object by heating is transferred to the thermal store of the object. This energy is shared across the kinetic energy stores of the particles in the object.

The particles in the part of the object being heated vibrate more and collide with each other. These collisions cause energy to be transferred between particles kinetic energy store. This is conduction

Convection is where energetic particles move away from hotter to cooler regions 

Convection can happen in gases and liquids

Liquids and gases are able to move. When you heat a region of a gas or liquid, the particles move faster and the space between particles increases 

This means the density of the region being heated to decrease

Because liquids and gases can flow, the warmer and less dense region will rise above denser cooler regions. 

If there is a constant heat source, a convection current can be created

Radiators create convection currents 

Heating a room with a radiator relies on creating convection currents in the air of the room

Energy is transferred from the radiator to air particles by conduction 

The air by the radiator becomes warmer and less dense

This warm air rises and is replaced by cooler air. The cooler air is then heated. The cycle repeats itself. 

Place a small beaker into a larger beaker.

Fill the small beaker with hot water from a kettle.

Put a piece of cardboard over the beakers as a lid. The lid should have a hole suitable for a thermometer.

Place a thermometer into the smaller beaker through the hole.

Record the temperature of the water in the small beaker and start the stopwatch.

Record the temperature of the water every 2 minutes for 20 minutes.

Repeat steps 1-6, each time packing the space between the large beaker and small beaker with the chosen insulating material.

Wrap a sheet of newspaper around a 100 ml beaker.
Fill the beaker with hot water from a kettle.

Put a piece of cardboard over the beaker as a lid. The lid should have a hole suitable for a thermometer.

Place a thermometer into the beaker through the hole.
 

Record the temperature of the water in the beaker and start the stopwatch.

Record the temperature of the water every 2 minutes for 20 minutes.

Repeat steps 1-6, each time adding another layer of newspaper around the beaker until there are 10 layers

Place the immersion heater into the central hole at the top of the block.

Place the thermometer into the smaller hole and put a couple of drops of oil into the hole to make sure the thermometer is surrounded by hot material.

Fully insulate the block by wrapping it loosely with cotton wool.

Record the temperature of the block.

Connect the heater to the power supply and turn it off after ten minutes.

After ten minutes the temperature will still rise even though the heater has been turned off and then it will begin to cool. 

This involves putting a lot of wind turbines up in exposed places like on moors or round coasts. 

Each turbine has a generator inside it which has rotating blades that turn the generator and produce electricity. 

There is no pollution

Spoil view and are noisy 

Initial costs are quite high but there are no fuel costs and minimal running costs. 

No permanent damage to the landscape.

Solar cells generate electric current directly from sunlight. They are often used in remote places. There is no pollution.

They are used to change batteries in calculators an watches

In sunny countries, solar power is a very reliable source of energy

You can't increase power output when there is extra demand

Initial costs are high but energy is free and running costs are almost nil

They only generate on a small scale

This is possible in volcanic areas or where hot rocks lie quite near to the surface

The source of much of the energy is the slow decay of various radioactive elements 

Very little damage to the environment and it is reliable 

The main drawback is that not many suitable locations for power plants and the costs to build a power plant are very high

It can be used to generate electricity or to heat building directly  

Hydroelectric power requires flooding a valley by building a dam. Water is allowed out through turbine there isn't as much pollution. It is reliable however no during a drought

It has a big impact on the environment due to flooding a valley. Possible loss of habitat for some species. 

An advantage is that it provides immediate response to an increased demand for electricity.

Initial costs are high but there is no fuel costs and minimal running costs.

it can only generate electricity on a small scale in remote areas. 

You need lots of small wave powered turbines located around located around the coast. They are connected to a generator. 

There is no pollution and unreliable since waves tend to die out.

The main problem is a disturbance to the seabed and the habitats of marine animals. Spoiling view is another problem and being a hazard to boats.

Initial costs are high but there are no fuel costs and minimal running costs.

Tides are used to generate electricity. Tidal barrages are big dams. Tides are produced by the gravitational pull of the sun and moon.

There is no pollution. 

The main problems are spoiling the view, altering habitats and preventing free access by boats.

Initial costs are moderately high but there are no fuel costs and minimal running costs

Tides are pretty reliable