P1: Energy

• d was
• o it
• 15 m/s
• Energy Stores and Systems

  Energy is just transferred between different stars and different
• Energy is Transferred Between Stores

  1. when energy is anaemad to an object, the energy stated in one of the object's sergustess

  2. The gates
• Energy Stores

  • Thermal energy stores
  • Gretational potential energy stores
  • Ed potential energy stores
  • Chemisel erg
  • Magesergy stores
  • Blastrustats energy shores
  • sy stores
• Energy is transformed many by force doing work), statically (work done by mixing charges), by heating or by cadation (e-light. p.70 or sound, p.88).
• System

  Just a fancy word for a single object (eg. the air in a piston) or a group of objects (eg two colliding vehicles) that you're interested in
• When a System Changes, Energy is Transferred

  1. Energy can be tranferred into or system, between different objects in the system or between different types of energy stores

  2. Closed systems we systems where neither matter or energy can enter or less

  3. The net change in the total energy of slosed tam is shaz10
• Energy can be Transferred by Heating


  1. Take the example of bong wader in a kettle-you can think of the water as the system. Energy is transferred to the water (from the kettle's heating element) by heating, into the water's thermal energy store (causing the temperaturs of the water to rise)

  2. You could also think of the kettle's heating element and the water together as a two object system. Energy is transferred electrically to the thermal energy store of the kettle's heating element, which transfers energy by heating to the water's thermal energy store
• Energy can be Transferred by Doing Work

  1. Work done is just another way of saying energy transferred-they're the same thing

  2. Work can be done when current flows (work is done against resistance in circuit, see p.24) or by a force moving an object (there's more on this on page 53)

  3. The initial force exerted by a person fo throw ball upwards does work. It causes an energy transfer from the chemical energy store of the person's arm to the kinetic energy store of the ball and arm

  4. A ball dropped from a height is accelerated by gravity. The gravitational force does work. It causes energy to be transferred from the ball's gravitational potential energy store to its kinetic energy store

  5. The friction between a car's brakes and its wheels does work as it slows down. It causes an energy transfer from the wheels' kinetic energy stores to the thermal energy store of the surroundings

  6. In a collision between a car and a stationary object, the pormal contact force between the car and the object does work. It causes energy to be transferred from the car's kinetic energy store to other energy stores, e.g. the elastic potential and thermal energy stores of the object and the car body. Some energy might also be transferred away by sound waves (see p.88)
• Kinetic energy

  E = ½mv^2
• A car of mass 2500 kg is travelling at 20 m/s. Calculate the energy in its kinetic energy store. E = ½mv^2 = ½ * 2500 * 20^2 = 500,000 J
• Raised Objects Store Energy in Gravitational Potential Energy Stores

  1. Lifting an object in a gravitational field requires work. This causes a transfer of energy to the gravitational potential energy (p.a.) store of the raised object

  2. The higher the object is lifted, the more energy is transferred to this store

  3. The amount of anergy in eg.p.e. store depends on the object's mass, ie height and the strength of the gravitational field the object is in (p.52)

  4. You can use this equation to find the ghenge in energy in an object's gravitational potential energy store for a change in height: E₁ = mgh
• Falling Objects Also Transfer Energy

  1. Whan something falls, energy from its gravitational potential mergy store is transferred to its kinetic energy store

  2. For a falling object when there's no air resistance, Energy lost from the g.p.e. store = Energy gained in the kinetic energy store

  3. In real life, it resistance (p.63) acts against all falling objects- it causes some energy to be transferred to other energy stores, e.g. the thermal energy stores of the object and surroundings
• Stretching can Transfer Energy to Elastic Potential Energy Stores


  1. Stretching or aquashing an object can transfer energy to the elastic potential energy store

  2. So long as the limit of proportionality has not been exceeded (p.55) energy in the elastic potential energy store of a stretched spring can be found using: E = ½ke^2
• Specific Heat Capacity

  The amount of energy needed to raise the temperature of 1 kg of a substance by 1°C
• Different materials have different specific heat capacities. For example, it takes 4200 J to warm 1 kg of water by 1°C, but only 1292 J to warm 1 kg of mercury by 1°C.
• Equation for change in thermal energy


  ΔE = mcΔθ
• You Can Investigate Specific Heat Capacities

  1. Measure the mass of the block, then wrap it in an insulating layer to reduce energy transferred from the block to the surroundings

  2. Insert the thermometer and heater

  3. Measure the initial temperature of the block and set the potential difference, V, of the power supply to 10 V. Turn on the power supply and start a stopwatch

  4. As the block heats up, take readings of the temperature and current, A, every minute for 10 minutes

  5. When you've collected enough readings, turn off the power supply. Using your measurement of the current, and the potential difference of the power supply, you can calculate the power supplied to the heater, using P=IV. You can use this to calculate how much energy E has been transferred to the heater at the time of each temperature reading using the formula E=Pt

  6. Plot a graph of energy transferred to the thermal energy store of the block against temperature. Find the gradient of the straight part of the graph. This is the specific heat capacity of the material of the block (gradient x the mass of the block)
• Energy can't be created or destroyed, only transferred or transformed.
• Conservation of Energy Principle

  Energy is a conserved quantity - it can be transferred usefully, stored, or dissipated, but it can never be created or destroyed.
• When energy is transferred, not all of it is transferred to where you want it to go. Some energy is always dissipated when an energy transfer takes place.
• In a closed system, the net change in energy is zero.
• Power

  The rate of energy transfer, or the rate of doing work. Measured in watts (J/s).
• A powerful machine is one which transfers a lot of energy in a short space of time.
• Conduction is the process where vibrating particles transfer energy to neighbouring particles.
• Convection is where energetic particles move away from hotter to cooler regions.
• Radiators Create Convection Currents

  1. Energy is transferred from the radiator to the nearby air particles by conduction

  2. The air by the radiator becomes warmer and less dense

  3. This warm air rises and is replaced by cooler air

  4. The cooler air is then heated by the radiator

  5. The previously heated air transfers energy to the surroundings (e.g. the walls and contents of the room), cools, becomes denser and sinks

  6. This cycle repeats, causing a flow of air to circulate around the room - this is a convection current