Physics Energy unit 1

The Storing of Energy

• Energy is added to your body's chemical store when you eat food.

• Energy is stored there until you need it.

• Your body then transfers it to your thermal store when you need to keep warm, or to your kinetic store to move about.

Internal energy

• The amount of energy in an object’s internal energy is the sum (total) of the kinetic energy and potential energy stored in the object's particles.

Internal energy and temperature

• The temperature of a body (object) is a measure of the energy in the kinetic stores of its particles.

• Increasing a body’s temperature increases the energy in the kinetic stores of the body’s particles, which means that the energy in the body’s internal store also increases.

System

A system is an object or group of objects.

There are changes in the way energy is stored when a system changes.

Kinetic energy equation + units

• Kinetic energy = ¹/₂ × mass × velocity²

• E_k = ¹/₂mv²

• Kinetic energy is in joules (J).

• Mass is in kilograms (kg).

• Velocity is in metres per second (m/s).

Gravitational potential energy equation + units

• Change in GPE = mass × gravitational field strength × change in height

• ΔE_p = mgΔh

• GPE is in joules (J).

• Mass is in kilograms (kg).

• Gravitational field strength is in Newtons per kilogram (N\kg).

• Height is in metres (m).

Elastic potential energy units

• EPE is in joules (J).

• The spring constant is in Newtons per metre (N/m).

• Extension is in metres (m).

Conservation of Energy

Energy cannot be created or destroyed. Energy can only be transformed from one store of energy into another.

Work done equation

• Work done = force x distance (moved along the line of action of the force).

Work done

The work done by a force is equal to the energy transferred to the object.

Power

Power is the rate of energy transfer (or work done).

The faster that energy is transferred (or work is done), the higher the power.

The power (measured in watts) is equal to the work done (in joules) divided by the time (in seconds).

P = W/T

Wasted Energy

When one store of energy is transferred to another, some energy is wasted. Wasted energy moves into unwanted stores of energy. The wasted energy dissipates (spreads out) to anything nearby.

Efficiency of Energy Transfer in joules

The efficiency of an energy transfer can never be more than 100.

• efficiency = useful output energy transfer/total input energy transfer

• The useful energy output and total energy input are measured in joules (J).

Efficiency (power in watts)

• Efficiency = useful power output/total power input

• The useful power output and total power input are measured in watts (W).

Reducing Unwanted Energy Transfer

Lubrication

reducing friction

thermal insulation

reducing energy transfer

thermal conductivity

Lubricants

• Lubrication reduces frictional forces.

• A moving object normally has at least one frictional force acting against it.

• The frictional force causes some energy to be lost.

Reducing friction

• Lubricants can reduce the friction between the surfaces of objects that are rubbing together.

• Lubricants are normally liquids.

Thermal insulation

• Heat will be lost through the roof, windows, walls and floor.

How to reduce Energy Transfer?

• Fit loft insulation (the roof).

• Use double glazing (windows).

• Use cavity wall insulation (walls).

• Fit carpets (floors)

Walls in homes

• We can decrease the rate a house cools down by:

• Having thicker walls.

• Having walls made from a material with a lower thermal conductivity.

Power - energy transfer

• Power (watts, W) = energy transferred (joules, J) ÷ time (seconds, s)

Power - work done

• Power (watts, W) = work done (joules, J) ÷ time (seconds, s)

Investigating Different Insulating Materials practical 2

The aim of this experiment is to investigate how well different materials reduce heat loss from a container of hot water, and identify which material is the most effective thermal insulator.

Equipment

• Two beakers (one large, one small)

• Kettle or hot water source

• Stopwatch

• Thermometer

• Measuring cylinder

• Cardboard lid with a hole for the thermometer

• Various insulating materials (e.g. bubble wrap, cotton wool, foil, felt)

Variables

• IV-Type of insulating material

• DV-Temperature change over time

• CV-Starting temperature, volume of water, type of beakers, room temperature

Method

1. Place a smaller beaker inside a larger beaker.

2. Measure a fixed volume of hot water and pour it into the smaller beaker.

3. Cover the beaker with the cardboard lid and insert a thermometer through the hole so it rests in the hot water.

4. Record the starting temperature of the water.

5. Start the stopwatch and record the temperature every two minutes for a total of 20 minutes.

6. Repeat the experiment using different insulating materials in the space between the two beakers.

Results

• Create a table showing temperature readings at each time interval.

• Use a line graph to plot temperature (°C) on the y-axis and time (minutes) on the x-axis.

• Draw a smooth curve for each material on the same graph to show how the temperature changes over time.

• Compare the cooling curves:

• The line that drops the slowest indicates the best insulator.

• The line that drops quickly represents a poor insulator.

Conclusion

• When the water is very hot, the temperature difference between the beaker and the air is large, so heat is lost quickly.

• Heat transfer is reduced when materials trap air, as air is a poor conductor of heat.

• The material that kept the water hottest for the longest time is the most effective thermal insulator.

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Safety and Precautions

• Hot water may cause burns or scalds:

• Pour carefully and never overfill the beaker.

• Beaker tipping over:

• Keep equipments away from edges and perform the experiment while standing.

• Steam from kettle:

• Possible burns allow water to cool slightly before pouring. Do not lean directly over the beaker

Energy Resources

• First, an energy resource is used to rotate a turbine.

• The rotating turbine rotates a coil of wire in a magnetic field (a generator).

• The coil of wire creates an electric current. The electric current is an energy carrier (or pathway) that can take the energy to your home.

Change in thermal energy units

change in thermal energy, ∆ E , in joules, J

mass, m , in kilograms, kg

specific heat capacity, c , in joules per kilogram per degree Celsius, J/kg °C

temperature change, ∆ θ , in degrees Celsius, °C

The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.

a resource is reliable if it can supply energy whenever demand appears — fossil and nuclear fuels are, wind and solar are not.

Uses of energy resources

Resource	Transport	Electricity generation	Heating
Coal	No	Yes — burned to raise steam for turbines	Yes — open fires, older boilers
Oil	Yes — petrol/diesel/kerosene (jet fuel)	Yes — oil-fired power stations	Yes — oil-fired boilers, kerosene heaters
Gas (natural)	Rare	Yes — gas-fired stations, quick to start	Yes — gas boilers, most UK home heating
Biofuel / biomass	Yes — biodiesel, bioethanol blends	Yes — biomass power stations	Yes — wood, pellets, biomass boilers
Nuclear fuel	No	Yes — heat to steam, no CO2 at point of use	No (heat is wasted to cooling)
Wind	No	Yes — wind turbines	No
Hydroelectric	No	Yes — falling water drives turbines	No
Tidal / wave	No	Yes — limited, but growing	No
Geothermal	No	Yes — some regions	Yes — direct ground heat, e.g. Iceland
Solar (PV / thermal)	Limited — solar cars, charging	Yes — PV panels, no turbine needed	Yes — solar water heating
Water (waves/tides/hydro)	No	Yes	No

Reliability: why some resources are more dependable

Resource	Reliable?	Reason (mark-scheme style)
Coal, oil, gas	Yes	Fuel can be stored and burned on demand; output controlled to match demand; not weather-dependent
Nuclear	Yes	Constant output, refuelled infrequently; high energy density per kg of fuel
Biofuel	Mostly	Can be stored and burned on demand, but supply limited by land and growing time
Wind	No	Output depends on wind speed; can be zero on still days; intermittent
Solar	No	Only generates in daylight; output falls in cloud and winter; zero at night
Hydro	Fairly	Dependable if reservoir is full, but drought reduces output; can be turned on quickly (pumped storage)
Tidal	Partly	Predictable timing, but only generates at certain points in the tide cycle
Geothermal	Yes (where available)	Heat flow is constant, but only viable in certain locations

Pros and cons

Resource	Pros	Cons
Fossil fuels	Reliable and can meet demand on demand; cheap per kWh; existing infrastructure	Finite; CO2 and SO2/NOx emissions; extraction damage
Nuclear	Reliable; high energy density; no CO2 at point of use; small fuel volume	Radioactive waste; decommissioning cost; high capital cost; accident risk; long build time
Wind	Renewable; no fuel cost; no CO2 in use	Intermittent/unreliable; visual and noise impact; high initial cost; needs backup
Solar	Renewable; no emissions in use; no moving parts; good for remote areas	Unreliable (night/cloud); low output per m2; high initial cost; needs large area
Hydro	Renewable; reliable when reservoir full; quick response; reservoirs for water supply	Flooding land and habitat loss; high build cost; drought risk; limited sites
Tidal/wave	Renewable; tides predictable; no fuel	Expensive; limited suitable sites; environmental impact on estuaries
Geothermal	Renewable; constant output; small land footprint	Only viable in volcanic/tectonic regions; drilling cost
Biofuel	Renewable if regrown; carbon-neutral in principle; storable	Land and water use competes with food; burning still releases CO2; deforestation risk

increase efficiency

How a power station works?

1. Fuel (coal, oil, gas, or nuclear) is burned to release energy as heat.

2. The heat boils water to make steam at high pressure.

3. The steam turns a turbine.

4. The turbine turns a generator, which produces electricity.

5. The steam is cooled and condensed, then reused.

Specific heat capacity units and meaning

E=mcΔθ,

• E — energy transferred, in joules (J)

• m — mass of the substance, in kilograms (kg)

• cc — specific heat capacity, in J/kg°C — the energy needed to raise 1 kg of the substance by 1°C

• ΔθΔθ — temperature change, in °C (final minus initial)