Waves
Concept
Explanation
Forces and waves Forces move a
meduim up and
down or back and
forth.A wave
moves forward.
Sketch
Direction of force
Direction of wave
Definition
A distubance that
transfer energy from
one place to another
Characteristics
Matter moves in place.
Energy travels entire
distance.
WAVE
Examples
Water wave
Sound wave
Nonexample
Ball rolling
Water rushing
Downstream
Waves transfer energy
•A wave is a disturbance
A wave is adisturbance that transfers energy from one place to
another.
Mechanical waves travel through a material,called a medium,
transferring energy.
When a mechanical wave travels through a medium,such as
water,ground,or air, the medium moves as the wave passes through
it,but is not permanently moved.After the wave has passed, the
medium returns to its former state.
Waves transfer energy
•Waves can be classified by how they move
A transverse wave travels in the direction perpendicular to the
disturbance that caused it.If you thrust your fist into a tub of water，
waves travel out from thedisturbance along the water's
surface.These waves move at right angles to the downward force
of your fist﹒
Waves transfer energy
• A longitudinal wave travels in the same direction as the
disturbance that caused it.If you lay a spring toy on its side and
push sharply on one end,waves will travel through the coils along
the length of the spring toy.In this example，the disturbance－the
push of your hand－is in the same direction in which the wave
moves down the spring toy.
Waves have measurable properties
•Waves have amplitude,wavelength,and frequency.
A wave has repeating crests and troughs, which alternate in a wave.
Wavelength is the distance from trough to trough or crest to crest.
Wavelength can be measured from any part of one wave to the
corresponding part on the next wave.
Amplitude is either how
high a wave peaks above
level(at its crests)or how
low it dips below level(at
its troughs)﹒
Waves have measurable properties
In a longitudinal wave such as in a spring toy, wavelength is the
distance between compressions or rarefactions.
Rarefactions are the spaces between compressions where the
medium is spread out.Amplitude describes how tightly bunched
the spring coils are in the wave.
• Frequency is the number of wavelengths that pass a fixed point in
a period of time－usually one second.
Question
• Write down two similarities and two differences between
transverse and longitudinal waves. Give one example of a
transverse wave and one example of a longitudinal wave.
Similarities ：
• Both carry energy from one point to another
• Both have a wavelength
Difference ：
• The movement in a transverse wave is at 90° to the motion while
in the longitudinal, the displacement is parallel
• There are regions of compression and rarefaction in a longitudinal
wave
Example of a transverse wave : light waves
Example of a longitudinal wave: Sound wave
Wave speed can be measured
•The formula for calculating the speed of a wave is
S = λ‧f
where S is speed，λis wavelength，f is frequency
Ex：A wave has a speed of 3 m/s and a frequency of 6(waves)/s.
What is its wavelength？
Ex：At what speed is the wave below traveling if it has a frequency
of 2/s？
1.2m
Ex：An ocean wave has a wavelength of 9 m and a frequency of
0.42/s. What is the wave’s speed？