BuilderGrades 6–8⏱ 15 min
Waves
Shake a rope and a spring. Change amplitude and frequency, measure the wavelength, and see that waves carry energy, not stuff.
Standards: MS-PS4-1MS-PS4-2
1Wonder
A surfer rides a wave that started hundreds of kilometres away. The water under the surfer didn’t travel all that way. So what did?
2Explore
This activity needs a bigger screen
Turn your phone sideways, or open this lesson on a tablet or computer. The explanation and quiz below work here.
Wavelength λ 4 m Speed v = f × λ 0.5 × 4 = 2 m/s
Try this
- Watch the red bead. Does it travel along the rope, or only go up and down?
- Make the amplitude bigger. What happens to the energy meter?
- Double the frequency. What happens to the wavelength λ?
- Look at the spring. Where are the coils squeezed together? This is how sound travels.
3Explain
Step 1 of 5
Waves carry energy, not stuff
As the wave passes, the red bead only moves up and down. The rope stays where it is. What travels along it is energy.
Describing a wave
A wave is described by its amplitude (energy), wavelength λ and frequency f. Waves carry energy from place to place without carrying matter along.
4Practice
Question 1 of 5
Which wave has the bigger amplitude?
5Recap
- Waves carry energy, not matter.
- Amplitude: how big the wave is. Bigger amplitude, more energy.
- Wavelength λ: crest to crest. Frequency f: waves per second (Hz).
- v = f × λ: on the same rope, higher frequency means shorter wavelength.
- Transverse waves move across (rope, light); longitudinal waves squeeze and stretch (sound).