# Forces and Energy

• Section 20 - Forces and Energy
• Energy transfers and systems
• Energy is transferred between stores mechanically, electrically, by heating or by radiation
• Kinectic, thermal, chemical, gravitational potential, elastic potential, electrostatic, nuclear, magnetic
• Energy is transferred between stores and objects in system
• Energy can be dissipated in wasteful ways too e.g. heat
• A closed system is defined so that the net energy change is 0
• If the system is a pan of water and camping stove, energy is transferred from the chemical store of the gas to the thermal store of the pan and water, increasing the temperature
• If the system is a box being lifted, energy is transferred to its kinetic and potential energy stores
• If the system is a toothbrush, energy is transferred from chemical store of the battery to the kinetic stores of the bristles. Energy is also dissipated by heat and sound.
• Work Done and Power
• Power = rate of energy transfer
• The larger the power of an object, the more work it does per second
• If a force moves an object, work is done
• Energy is transferred mechanically from one store to another
• Forces
• Contact forces when the objects are touching each other
• Non-contact forces have interacting fields but aren't touching
• Two objects feel an equal but opposite force, called an interaction pair, that can be shown by arrows
• Free-body force diagrams show all the forces acting upon an object or system with arrows of size relative to their magnitudes
• A resultant force is the overall force on a point or object
• Forces and Vector Diagrams
• Scale Drawings
• Draw all the forces acting on an object "tip to tail"
• Then draw a straight line from the first force to the end of the last force - this is the resultant force
• Measure the length to find the magnitude and the angle to find the direction
• If all of the forces on an object combine to give a resultant force of 0, the object is in equilibrium
• You can split a force into components and measure each one to measure the overall force

## Comments

No comments have yet been made

## Similar Science resources:

See all Science resources »See all Energy and efficiency resources »