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 Energy. Show all posts
Showing posts with label Energy. Show all posts
2009-05-20
2008-01-11
Understanding Waves
Waves
Understanding Waves
Wave and Energy
A Wave is a disturbance that transfers energy between 2 points through vibrations (or oscillations) in a medium, without transferring matter between the two points.
Example 1: When you hold the end of a rope and a friend of yours wave the rope at the other end up and down, then a wavy movement appears. This is a movement of the rope and it transfers energy but NOT the rope.
Example 2: When you throw a stone on the surface of a calm pond, a circular ripple will appear and subsequently other smaller ripple will appear from the point of origin, these waves will eventually turn into a few big circles which then encompass smaller circular ripples in the middle. What happen is, the kinetic energy from the stone is transferred to the water in the form of ripples, which is an example of wave.
There are two types of waves:
1. Transverse waves
2. Longitudinal waves
Transverse waves
Transverse wave is a wave in which direction of vibration is perpendicular to the direction of movement of wave.
Examples are : water waves, waves on a string, radio waves, light waves and electromagnetic waves.
Longitudinal waves
Longitudinal wave is a wave in which the direction of vibration is parallel to the direction of travel of the wave
Examples are: sound waves and waves on a slinky spring.(which consists of regions of rarefaction and compression).
Wavefronts
Wavefront is a line that joins all the points vibrating in phase, such as a line passing through similar wave crests. It consists of crest and trough. Crest is the peaky part of the wave and trough is the lowest part of the wave.
Wavefront is perpendicular to the direction of wave movement.
Oscillating System:
Waves are produced by oscillating systems (or vibrations) in a medium.
An oscillation is a to and fro movement along a fixed path.
Examples are: Swinging pendulum(horizontally) and a Spring swinging up and down (vertically).
What u must now is that:
One complete oscillation is a to and fro movement of a body when it has returned to its original position and is moving in the same original direction.
Amplitude, a, is the maximum displacement from the resting position.
Period, T, is the time taken to make one complete oscillation.
Frequency, f, is the number of oscillations produced in one second.
Understanding Waves
Wave and Energy
A Wave is a disturbance that transfers energy between 2 points through vibrations (or oscillations) in a medium, without transferring matter between the two points.
Example 1: When you hold the end of a rope and a friend of yours wave the rope at the other end up and down, then a wavy movement appears. This is a movement of the rope and it transfers energy but NOT the rope.
Example 2: When you throw a stone on the surface of a calm pond, a circular ripple will appear and subsequently other smaller ripple will appear from the point of origin, these waves will eventually turn into a few big circles which then encompass smaller circular ripples in the middle. What happen is, the kinetic energy from the stone is transferred to the water in the form of ripples, which is an example of wave.
There are two types of waves:
1. Transverse waves
2. Longitudinal waves
Transverse waves
Transverse wave is a wave in which direction of vibration is perpendicular to the direction of movement of wave.
Examples are : water waves, waves on a string, radio waves, light waves and electromagnetic waves.
Longitudinal waves
Longitudinal wave is a wave in which the direction of vibration is parallel to the direction of travel of the wave
Examples are: sound waves and waves on a slinky spring.(which consists of regions of rarefaction and compression).
Wavefronts
Wavefront is a line that joins all the points vibrating in phase, such as a line passing through similar wave crests. It consists of crest and trough. Crest is the peaky part of the wave and trough is the lowest part of the wave.
Wavefront is perpendicular to the direction of wave movement.
Oscillating System:
Waves are produced by oscillating systems (or vibrations) in a medium.
An oscillation is a to and fro movement along a fixed path.
Examples are: Swinging pendulum(horizontally) and a Spring swinging up and down (vertically).
What u must now is that:
One complete oscillation is a to and fro movement of a body when it has returned to its original position and is moving in the same original direction.
Amplitude, a, is the maximum displacement from the resting position.
Period, T, is the time taken to make one complete oscillation.
Frequency, f, is the number of oscillations produced in one second.
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