Conceptual Physics - Chapter 9: Energy

Terms in this set (26)

Work
The product of the net force on an object and the distance through which the object is moved. work = net force x distance, W = Fd
joule
unit of measurement for work, the newton-meter (N×m)
When is work done on an object?
When a force acts on an object and the object moves in the direction of the force.
Power
The rate at which work is done.
How can you calculate power?
Power equals the amount of work done divided by the time interval during which the work is done.
power = work done / time interval, P = W/t
Watt
unit of measurement for power, joule per second
Energy
The property of an object or system that enables it to do work. Like work, it is measured in joules.
Mechanical energy
The energy due to the position of something or the movement of something.
What are the two forms of mechanical energy?
Kinetic energy and potential energy.
Potential Energy
Energy that is stored and held in readiness.
Elastic Potential Energy
A mechanical form of stored energy such as a stretched or compressed spring, a drawn bow or a stretched or twisted rubber band.
Chemical Energy
Any substance that can do work through chemical reactions possesses chemical energy such as in fuels, electric batteries and food.
Gravitational Potential Energy
Potential energy due to elevated positions. PE = weight x height or PE = mgh
Name three examples of potential energy
Elastic, Chemical, and Gravitational
Kinetic energy
Energy of motion. Kinetic energy of an object is equal to half the mass multiplied by the square of the speed.
kinetic energy = ½mass x speed²
KE = ½mv²
How are work and the kinetic energy of a moving object related?
The kinetic energy of a moving object is equal to the work required to bring it to its speed from rest, or the work the object can do while being brought to rest. Fd = ½mv²
Work-Energy theorem
Whenever work is done, energy changes. Work = ∆KE
Law of Conservation of Energy
Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.
Machine
A device used to multiply forces or simply change the direction of forces.
How does a machine use energy?
A machine transfers energy from one place to another or transforms it from one form to another.
Lever
A simple machine made of a bar that turns about a fixed point.
Fulcrum
The pivot point of the lever.
Mechanical Advantage
The ratio of output force to input force.
MA =Output Force / Input Force
Pulley
A kind of lever that can be used to change the direction of a force.
Why can't a machine be 100% efficient?
Some energy is transformed into atomic or molecular kinetic energy - making the machine warmer.
Efficiency
The ratio of useful energy output to total energy input.
efficiency = useful work output / total work input
It can also be expressed as the ratio of actual mechanical advantage to theoretical mechanical advantage.
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