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Cause and Effect — work, energy and machines
Cause
A force does work on an object by displacing it in the direction of the force
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Work-energy theorem
the work done equals the change in the object's energy
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Effect: energy is gained, stored or transferred — and machines let us apply that work more conveniently, never creating energy
Work, Energy, and Simple Machines
work transfers energy — machines just make it easier
7.1
Work Done by a Constant Force
W = F × s · joule · zero work · positive and negative work
7.2
The Work-Energy Theorem
work done = change in energy · energy · joule (J)
7.3
Forms of Energy
mechanical · thermal · light · sound · electrical · nuclear · chemical
7.4
Mechanical Energy
kinetic energy ½mv² · potential energy mgh · conservation of mechanical energy
7.5
Power
P = W/t · watt · 1 W = 1 J s⁻¹ · horsepower
7.6
Simple Machines
effort · load · mechanical advantage · pulley · inclined plane · lever
- Work
- Work is done by a force on an object when the force displaces the object in the direction of the force.
- Energy
- An object having the capacity to do work is said to possess energy.
- Work-energy theorem
- The work done on an object or a system is equal to the change in its energy.
- Kinetic energy
- The energy possessed by an object due to its motion; K = ½mv².
- Potential energy
- The energy stored by an object due to its deformation, or in a system of objects due to their relative positions; gravitational PE = mgh.
- Power
- The rate at which work is done; P = W/t, measured in watts.
- Simple machines
- Devices that make work easier by changing the magnitude or direction of the force, though they do not reduce the total work done.
- Joule (J)
- The SI unit of work and of energy. 1 J of work is done when a force of 1 N displaces an object by 1 m in the direction of the force.
- Positive work
- Work done when the displacement is in the same direction as the applied force.
- Negative work
- Work done when the displacement is in the direction opposite to the applied force.
- Gravitational potential energy
- The energy stored in the Earth-object system because of the object's height; U = mgh near the Earth's surface.
- Mechanical energy
- The sum of the kinetic energy and the potential energy of an object.
- Conservation of mechanical energy
- The mechanical energy of an object stays constant if no other external force acts on it.
- Watt (W)
- The SI unit of power; 1 W = 1 J s⁻¹. One horsepower is 746 W.
- Effort and load
- The effort is the force we apply to a machine; the load is the force that has to be overcome.
