Mechanics Flashcards
Work is done whenever…
Energy is transferred
What is needed to move something?
- Usually you need a force to move something because you’re having to overcome another force.
-The thing being moved has kinetic energy while its moving. - — The kinetic energy is transferred to another form of energy when the movement stops
Define the word ‘work’
The word work in physics means the amount of energy transferred from one form to another when a force causes a movement of some sort
What is the equation used to calculate the work done?
- Work done (W) = Force causing motion (F) * distance moved (s)
- W = Fs
What is work done measured in?
Joules
What is force measured in?
Newtons
What is distance measured in?
Metres
What are the key points to remember about the W=Fs equation?
1- Work is the energy that’s been changed from one form to another - it’s not necessarily the total energy. E.g. moving a book from a low shelf to a higher one will increases its gpe but it had some gpe to start with. Here the work done would be the increase in gpe, not the total gpe
2- The distance needs to be measured in metres
3 - The force F will be a fixed value in any calculations either because its constant or because its the average force
4 - The equation assumes that the direction of the force is the same as the direction of movement
5 - The equation gives you the definition of the joule,
‘One joule is the work done when a force of 1 newton moves an object through a distance of 1 metre’
Which formula is used to calculate the work done when the direction of movement is different to the direction of the force?
W=FsCosθ
In the formula W=FsCosθ what is θ?
θ is the angle between the direction of the force and the direction of motion
When calculating work done where the direction of movement is different to the direction of the force which force should be used in the equation?
The force which is causing the motion
What is the area under a force-distance graph equal to?
The work done
How can work done be calculated from a force-distance graph?
By calculating the area under the graph
If a force-distance graph is irregular shaped how can the area underneath it be calculated?
The graph can be split into shapes and the area of each individual shape can be calculated
Define power
Power is the rate of doing work - it is the amount of energy transferred from one form to another per second
What equation can be used to calculate power given work done and time?
Power = Change in energy (work done) / change in time
P = ΔW/Δt
Define the watt
The watt is a rate of energy transfer equal to 1 joule per second
What is the equation for calculating power given force and velocity?
Power = Force * Velocity
P=Fv
Define the principle of conservation of energy
Energy cannot be created or destroyed. Energy can be transferred from one form to another but the total amount of energy in a closed system will not change
What is the equation used to calculate efficiency?
Efficiency = Useful output power / Input power
How can you get efficiency as a percentage?
You can multiply the efficiency by 100 to get it as a percentage
What is kinetic energy?
Kinetic energy is the energy of anything moving
What is the formula for calculating kinetic energy and what are each of the variables?
Ek = 1/2mv^2
- v is velocity
- m is mass
What are the different types of potential energy?
Gravitational and elastic
What is gravitational potential energy?
Gravitational potential energy is the energy something gains if you lift it up
What is the formula for calculating gravitational potential energy and what are each of the variables?
ΔEp = mgΔh
- m is the mass of the object
- Δh is the height the object is lifted
- g is the gravitational field strength
What is elastic strain energy? (elastic potential energy)
Elastic strain energy is the energy you get in say a stretched rubber band or spring
What is the formula for calculating elastic strain energy and what are each of the variables?
E = 1/2kΔl^2
- Δl is the extension of the spring
- k is the spring constant
