SP8 Forces doing work/SP9 Forces and their effects Flashcards
What happens to energy when a system changes?
It gets transferred from one form to another
Define closed system
System which experiences no external forces
Define work done
When external forces transfer energy into a system
How do we calculate work done?
force x distance moved in the direction of the force
Define power
- Rate at which energy is transferred
- can also be the rate of doing work when energy is being transferred by forces
- measured in watts W
State the equation for power
work done/time taken
What are the units for work done?
Joules
Define efficiency
Measure of how much energy is not lost as waste
State some examples of non contact forces
- gravitational attraction
- electrostatic attraction
- magnetic attraction
State some examples of contact forces
- normal contact force
- friction
Define normal contact force
Force acts at right angles to the surface that it is touching
Define action reaction forces
Pairs of forces acting on different objects in opposite directions
Define force field and give examples
Space around an object where it can affect other objects
eg: magnetic field for magnets and electric field for static electricity
What is the difference between a vector and a scalar quantity?
A vector quantity has magnitude and direction, whereas scalar quantities only have magnitude
Define scale diagrams
A way of working out the resultant forces or component forces by drawing a diagram where the lengths of arrows represent the sizes of the forces.
What does the length of the arrow represent in scale diagrams?
Its size
–> so direction with larger arrows shows resultant forces
What do equal arrows in opposite directions represent in a scale diagram?
- equal in magnitude but opposite in direction
- so the object is in equilibrium
- so it travels at a constant velocity
What do free body diagrams represent?
A diagram of an object showing all the forces acting on it and the size and direction of those forces.
What direction is the reaction force going to be in a free body diagram?
At right angles to the line of contact
Define moment
A turning force
What does the moment of a force depend on?
The size of the force and where it is applied
State the equation for moment
force x perpendicular distance from pivot
Describe what happens to the moments in a system when it is balanced
The sum of clockwise moments = sum of anticlockwise moments
Define lever
A bar that pivots around a point and is used to transfer a force
Define pivot point
A point which an object can rotate about but cannot move away from
What does a gear affect?
Speed, force or direction
What direction will the second gear turn towards?
The opposite direction to that of the first gear
What are the effects of lubrication?
Reduces friction so will reduce unwanted energy
