Work
1. Work is done when a force is exerted to move an object through a distance in the direction of the force.
2. Work, W, is defined as product of the force and the displacement of an object in the direction of the force.
Work=Fs
Where,
F= the force acting
S= the displacement (or distance traveled in the direction of the force)
3 .Work is a scalar quantity and its unit is joule (J) or N m. 1 joule =1Nm
Example:
A block which is at rest is acted on by force of magnitude 3 N in different direction. Determine the wok done by the block in each case.
a) The force act from the left, the object move to the right for 2 m.
b) The force act from the right, the object to the left for 2 m.
Solution
a) F=3 N
Moving to the right for 2m.
Work done, FS = 3 x 2
= 6Nm
b) F= -3 N
Moving to the left for 2 m (negative
sign indicates object move to the left)
Work done = FS = -3 X -2
= -3 N x (-2m)
=6 Nm
5 .1 joule is the work done when a force of 1 Newton moves of an object for 1 m in the direction of the force .
6 . Work is not done when a force is exerted on an object but the object does not move.
7 . In conclusion, work is not done when:
a) The direction of motion is perpendicular to the direction of the force exerted
b) Force is exerted on the object but the object does not move.
Energy
1. We need energy to do work.
2. Energy is defined as the Potential or the ability to do work.
3. Energy is scalar quantity and its unit is the joule (J) or N m.
4. Energy can exist in various form. Examples potential energy, kinetic energy, heat energy, electrical energy and sound energy.
5. Energy cannot be created or destroyed. The work done related to the change of the form of the energy.
Example
A student of mass 50 kg walks up a flight of stairs 1.5 m high. What is…
a) the work done by the student?
Work = Fx s
=mg x s
=(50 x 10) N x 1.5 m
=750 J
b) energy needed = work done
=750 J
Showing posts with label Work. Show all posts
Showing posts with label Work. Show all posts
2009-05-20
2007-09-19
WORK
Here is the simplification of explanation for Work, Energy, Power and Efficiency
Work, Energy, Power and Efficiency
Work
1. Work is defined as the product of the applied force and the displacement of an object in the direction of the applied force.
2. W = F x S
3. W= work done, F = force applied, S = displacement in the direction of force.
4. SI unit for work = Joule (J), other unit = Nm
5. Work is not done when:
a. The object is stationary aka not moving
b. No force is applied on the object in the direction of displacement.
c. The direction of motion of the object is perpendicular to that of the applied force.
6. When work is done to an object, energy is transferred to the object.
Energy (Energy is the capacity to do work)
1. Energy exists in different forms: kinetic energy, gravitational potential energy, elastic potential energy, sound energy, heat energy, light energy, electrical energy and chemical energy.
2. The unit for energy is Joule (J) – same as work
3. The work done is equal to the amount of energy transferred.
4. Kinetic energy is the energy of an object due to its motion.
5. Kinetic energy or work done is given by:
a. ½ Mv2
b. M = mass, v = velocity
c. Unit: Joule /
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6. Gravitational potential energy is the energy of an object due to its higher position in the gravitational field.
a. E = mgh
b. M = mass, g = acceleration due to gravity, h = height in metre
Conservation of energy
1. The principle of conservation of energy states that energy cannot be created or destroyed but can change from one form to another form of energy.
2. Total amount of energy remains the same.
3. When water falls from a dam, its potential energy changes to kinetic energy.
4. When a swing moves from one position to another position, its potential energy changes to kinetic energy alternately.
Power
1. Power is defined as the rate of doing work.
a. Power = (Work / Time)
b. P = power, W = work, T = time
2. SI unit for work is = watt (W).
Efficiency
1. Efficiency of a device is defined as the percentage of the energy input that is transformed into useful energy.
2. Efficiency = (useful Energy output / Energy input ) X 100%
a. Efficiency = (Useful power output / Power input) X 100%
b. Unit is given in percentage.
You must know the importance of maximising the efficiency of device.
Work, Energy, Power and Efficiency
Work
1. Work is defined as the product of the applied force and the displacement of an object in the direction of the applied force.
2. W = F x S
3. W= work done, F = force applied, S = displacement in the direction of force.
4. SI unit for work = Joule (J), other unit = Nm
5. Work is not done when:
a. The object is stationary aka not moving
b. No force is applied on the object in the direction of displacement.
c. The direction of motion of the object is perpendicular to that of the applied force.
6. When work is done to an object, energy is transferred to the object.
Energy (Energy is the capacity to do work)
1. Energy exists in different forms: kinetic energy, gravitational potential energy, elastic potential energy, sound energy, heat energy, light energy, electrical energy and chemical energy.
2. The unit for energy is Joule (J) – same as work
3. The work done is equal to the amount of energy transferred.
4. Kinetic energy is the energy of an object due to its motion.
5. Kinetic energy or work done is given by:
a. ½ Mv2
b. M = mass, v = velocity
c. Unit: Joule /
-->
kgm2s-2
6. Gravitational potential energy is the energy of an object due to its higher position in the gravitational field.
a. E = mgh
b. M = mass, g = acceleration due to gravity, h = height in metre
Conservation of energy
1. The principle of conservation of energy states that energy cannot be created or destroyed but can change from one form to another form of energy.
2. Total amount of energy remains the same.
3. When water falls from a dam, its potential energy changes to kinetic energy.
4. When a swing moves from one position to another position, its potential energy changes to kinetic energy alternately.
Power
1. Power is defined as the rate of doing work.
a. Power = (Work / Time)
b. P = power, W = work, T = time
2. SI unit for work is = watt (W).
Efficiency
1. Efficiency of a device is defined as the percentage of the energy input that is transformed into useful energy.
2. Efficiency = (useful Energy output / Energy input ) X 100%
a. Efficiency = (Useful power output / Power input) X 100%
b. Unit is given in percentage.
You must know the importance of maximising the efficiency of device.
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