7th Grade Science Final Study Guide

  1. A sound wave traveling through a solid material has a frequency of 250 hertz. The wavelength of the sound wave is 2 meters. What is the speed of sound in the material?

Speed = wavelength x frequency Speed = 2meters x 250 Hz = 500 m/s

  1. A tuning fork is used to produce sound waves with a frequency of 220 hertz. The waves travel through the air at 340 m/s. What is the wavelength of the sound wave?

Wavelength = speed/frequency Wavelength = 340/220 = 1.55 meters

  1. What is the frequency of ocean waves that have a speed if 20 m/s and a wavelength of 50 m?

Frequency = speed/wavelengthFrequency = 20/50 = 0.4 Hz

  1. A radio station transmits to a receiving antenna. What type of wave is the radio wave?

Radio waves are transverse waves and electromagnetic waves.

  1. A student shakes the end of a rope with a frequency of 2.0 hertz, causing waves with a wavelength of 0.9m to travel along the rope. What is the velocity of the wave?

Speed = wavelength x frequencySpeed = 0.9 x 2.0 = 1.8 m/s

  1. On end of a horizontal string is caused to oscillate vertically while the other end is attached to a fixed object. What type of wave travels along the string?

A transverse wave travels along the string.

  1. Why would astronauts on the moon not be able to hear a landslide (think about air molecules)?

Because sound waves need a medium to travel through (they are mechanical waves)and there is no medium (air) in space. If there are any air molecules in space, they are too far apart in space for the sound to be able to travel.

  1. How are radio waves, visible light, and x-rays the same in a vacuum?

They all travel the same speed (speed of light).

  1. Where can sound waves not travel?

Sound waves cannot travel in a vacuum (such as outer space).

  1. What is a rarefaction? Give an example.

A rarefaction is a part of a compressional wave where the particles are more spread out.

  1. Where does visible light fall on the electromagnetic spectrum?

On the electromagnetic spectrum, visible light is between infrared and ultraviolet.

  1. In regards to light, why would a tree on a distant hillside appear green?

The tree appears green because all colors of light are absorbed except green. Green light is reflected.

  1. Why would a spoon appear to be broken when it enters water?

The spoon appears to be broken because of refraction. Refraction happens when light travels from one medium to another and changes speed and bends. This also causes objects to look different sizes and shapes when they are submerged in water.

  1. How does a mirror reflect light?

The light is reflected at the same angle at which it hit the mirror.

  1. What happens to green light and red light when they shine on a green leaf?

The red light will be absorbed and the green light will be reflected. That’s why we see green.

  1. On a warm sunny afternoon, ocean water splashed onto a rock. A short time later, the rock was dry. What happened to the water on the rock?

The water evaporated because it absorbed heat. It changed from a liquid to a gas.

  1. What are the characteristics of a solid? Liquid? Gas?

Solids- particles packed tightly, particles stay in a fixed position and vibrate, particle have low energy and can’t move around much, particles remain in a fixed shape

Liquids- particle farther apart, particles slip and slide past each other, particle move more, particles have more energy and take the shape of the container

Gases- particles are very far apart, particle move freely and have high energy, particle can go wherever they want and will take the shape of the container if they are in a closed container

  1. A glass of ice water is placed on a table. After 10 minutes, there are drops of water on the outside surface of the glass. Which change in phase caused the drops of water?

Condensation- water vapor (gas) from the air hits the cold glass and turns to a liquid

  1. The moon has a smaller mass than the Earth. If you were able to travel to the moon, what would happen to your weight?

Your weight would be less because the moon has less mass than the Earth and less gravity.

  1. Describe the molecules of a solid, liquid, and gas.

See number 17

  1. If you were able to go to the top of a building and drop an apple and basketball at the same time, why would both hit the ground at about the same instant?

They would both hit at about the same time because the force of gravity is the same on all objects on Earth.

  1. Why must the space shuttle use great force to get into outer space?

The space shuttle must use great force to get into outer space because it must escape Earth’s gravity.

  1. Describe what happens as water turns to ice.

The particles cool down and slow down. The arrangement of molecules changes as they pack more tightly together. They become fixed in position and vibrate.

  1. The force of gravity on the surface of the moon is about one-sixth the force of gravity on the surface of Earth. Which describes the relationship of mass and weight of an object on the moon compared to that on Earth?

The weight on the moon would be less because the moon has a smaller mass and less gravity than Earth. Your mass would stay the same because your mass doesn’t change o matter where you are.

  1. A student rapidly rubs the palms of both hands together. What type of energy transformations occur?

The energy transformations that occur are:

Chemical (in food)  mechanical (of hands moving)  thermal (heat)

  1. Bob threw a ball into the air. It followed a curved path and fell to the ground. Explain why this happened.

The ball began to fall back to the ground due to the force of gravity.

  1. What is a good conductor of heat and electricity? What is a poor conductor of heat and electricity?

A good conductor lets heat travel through it easily and will get hot quickly. An example would be metal.

A poor conductor does not let heat travel through it easily. It will heat up very slowly/stay cool longer. An example would be rubber or glass.

  1. Explain heat transfer, including the movement of molecules.

Heat always travels from hot to cold. When cooking, heat travels from the oven  pan  food

  1. When an electric fan is running, most of the incoming electrical energy changes into which kind of energy?

Electrical  mechanical (of the fan blades moving)

  1. Which type of energy transfer occurs when a beaker of water is heated on a hot plate?

Electrical  heat

  1. A pendulum swings as shown in the diagram. At which position is the kinetic energy of the pendulum bob least?

The kinetic energy would be the least at point C. The higher up the pendulum, the more potential energy and the less kinetic energy.

  1. What happens to the potential energy of the apple as it approaches the ground?

Since potential energy increases as an object moves higher, as the pendulum approaches the ground, the potential energy would decrease and the kinetic energy would increase.

  1. As a pendulum moves from the bottom of its swing to the top of its swing, what happens to the kinetic energy? Potential energy?

As he pendulum moves higher, its kinetic energy will decrease and its potential energy will increase because things that are higher up have more potential energy.

Where is the crest and trough? The crest is a high point of a wave and the trough is a low point of the wave. A wavelength is from crest to crest or trough to trough

  1. Which type of waves require a medium?

Mechanical waves such as sound waves require a medium.

  1. What is the unit of wavelength?

meters

  1. Where is the rarefaction on the following wave?
  1. Black objects absorb most colors that hit them and reflect very little so they will be warmer.
  2. White objects reflect most colors that hit them and absorb very little so they will be cooler.