Grade 4 Science Practice Test: Waves, Sound and Sending Information

A wave moves energy forward. The water or air it passes through mostly moves back and forth or up and down, then stays behind.

Amplitude measures how far the wave rises from its rest position. The distance from crest to crest is the wavelength, and the lowest point is the trough.

Wavelength is the distance from one crest to the next, so 4 meters is longer than 2 meters. The amplitudes are the same because the waves are equally tall.

A harder hit gives the drum skin more energy, so it moves farther back and forth. Bigger vibrations make sound waves with a larger amplitude, which we hear as louder.

A wave with a larger amplitude carries more energy, so it can push more sand and wear away more of the coast.

Long and short blinks form a code that the other ship can read. The other choices are things that happen, but no one is sending information.

Two long whistles mean "wait" and two short whistles mean "go," in that order. "Go, then wait" reads the signals backward.

Phones turn pictures into a long pattern of on-and-off signals. The receiving phone decodes the pattern and shows the picture again.

Flags need light to be seen, so they fail at night. Sound from a drum travels in the dark, so the drum code can still carry the message.

In a code, each pattern stands for something, like a letter. Both people know the code, so the receiver can turn the pattern back into words.