Forces And Energy

• What is the principle regarding energy usage mentioned on pages 156 and 157?

  Energy is never used up, only transformed.
• What are the different energy stores mentioned?

  • Chemical energy stores
  • Kinetic energy stores
  • Thermal energy stores
  • Gravitational potential energy stores
  • Elastic potential energy stores
  • Electrostatic energy stores
  • Magnetic energy stores
  • Nuclear energy stores
• How is energy transferred between stores?

  Energy is transferred mechanically, by heating, or by radiation.
• What defines a system in physics?

  A system is a single object or group of objects.
• What happens to energy when a system changes?

  Energy is transferred into or away from the system.
• What is an ideal system in terms of energy change?

  An ideal system has a net change in energy of zero.
• How is energy transferred when heating a pan of water on a stove?

  Energy is transferred into the thermal energy stores.
• What occurs when a box is lifted off the floor?

  Work is done against gravity, transferring energy.
• What is the formula for kinetic energy?

  $KE =$$\frac{1}{2}mv^2$
• What is the formula for gravitational potential energy?

  $\Delta GPE =$$mg\Delta h$
• How do electrical devices transfer energy?

  They transfer energy between different energy stores.
• How does an electric toothbrush function as a system?

  It transfers energy from the battery to the bristles.
• What happens when a box is dropped?

  Gravitational force does work transferring energy.
• What does a hair dryer do as a system?

  It transfers energy electrically to the fan and heating element.
• What is the definition of work in physics?

  Work is done when a force moves an object.
• How is work calculated in physics?

  Work done = Force x Distance.
• What is the unit of work done?

  Joule (J)
• How much work is done when a force of 70 N lifts a tyre 1.2 m?

  84 J
• What happens to energy when work is done against friction?

  Some energy is dissipated as thermal energy.
• What is the definition of power in physics?

  Power is the rate of energy transfer.
• What is the unit of power?

  Watt (W)
• How do you calculate power?

  Power = Work done / Time taken.
• If a motor does 4.8 kJ of work in 2 minutes, what is its power output?

  40 W
• What is a force in physics?

  A force is a push or pull on an object.
• What is the purpose of a free body force diagram?

  It shows all forces acting on an isolated body.
• What is the resultant force?

  The resultant force is the overall force on an object.
• What does it mean for an object to be in equilibrium?

  It means the resultant force on it is zero.
• How can you find a missing force in equilibrium?

  Draw known forces and complete the triangle.
• How can you split a force into components?

  By drawing it at right angles on a scale grid.
• What do the components of a force represent?

  They represent the same effect as the single force.