2 Concept Explanation Sketch Forces and waves Forces move a meduim up and down or back and forth.A wave moves forward.Direction of forceDirection of wave
3 DefinitionA distubance that transfer energy from one place to anotherCharacteristicsMatter moves in place.Energy travels entire distance.ExamplesWater waveSound waveNonexampleBall rollingWater rushingDownstreamWAVE
4 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.
5 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﹒
6 Waves transfer energyA 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.
7 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)﹒
8 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.
9 Frequency is the number of wavelengths that pass a fixed point in a period of time－usually one second.QuestionWrite 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.
10 Similarities ：Both carry energy from one point to anotherBoth have a wavelengthDifference ：The movement in a transverse wave is at 90° to the motion while in the longitudinal, the displacement is parallelThere are regions of compression and rarefaction in a longitudinal waveExample of a transverse wave : light wavesExample of a longitudinal wave: Sound wave
11 Wave speed can be measured The formula for calculating the speed of a wave isS = λ‧fwhere S is speed，λis wavelength，f is frequencyEx：A wave has a speed of 3 m/s and a frequency of 6(waves)/s. What is its wavelength？
12 Ex：At what speed is the wave below traveling if it has a frequency of 2/s？ 1.2mEx：An ocean wave has a wavelength of 9 m and a frequency of 0.42/s. What is the wave’s speed？