Section 20 - Forces and energy - Energy transfers, systems, work done, power and force Flashcards
What happens to the energy when a system changes?
Transferred into or away from the system
Dissipated or stored in less useful energy stores
4 ways energy can be transferred between stores?
Mechanically (by forces doing work), electrically (by a moving charge doing work), by heating or by radiation
When a pan of water is heated on a gas camping stove and the system is the pan of water, how is energy transferred into the system?
Energy transferred into system by heating to thermal energy stores of pan and water, which increases temperature.
When a pan of water is heated on a gas camping stove and the system is the camping stove and pan, how is energy transferred?
Energy transferred from chemical energy store of gas to thermal energy stores of pan and water, increasing temperature
When the box is the system, how is energy transferred when a box is lifted off of the floor?
As box lifted, work is done against gravity. This causes energy to be transferred to box’s kinetic and GPE stores
How do electronic devices transfer energy to work?
By transferring energy between different energy stores
When an electric toothbrush is the system, how is energy transferred?
Transfers energy electrically from chemical energy store of battery to kinetic energy store of bristles. Some energy transferred out of system to surroundings by sound and by heating
What happens on an object when a force moves the object through a distance?
When a force moves an object through a distance, work is done on the object and energy is transferred
Equation for work done?
Work done (J) = Force (N) x Distance moved in direction of force (m) E = F x d
What happens to energy being transferred when you push something along a rough surface?
When you push something along rough surface, you do work against frictional forces. Energy transferred to kinetic energy store of object and some transferred to thermal energy stores due to friction, causing increase in overall temperature of object
What is power?
How much work is done per second
The rate of energy transfer
Equation for power?
Power (W) = work done (J) ÷ time taken (s)
P = E ÷ t
What do interacting magnetic fields cause between magnetic objects and electrostatic forces between electrical charges?
Attraction and repulsion
What is an interaction pair?
Whenever two objects interact, they feel an equal and opposite force (Newton’s 3rd law)
What does a free body force diagram show?
All the forces acting on an isolated object
