The Doppler effect, named for Austrian scientistChristopher Doppler, who described it in 1842, is a change in the frequency of a wave due
to motion of the source relative to the observer. You can detect the Doppler effect whenever an object that makes a constant sound is moving
relative to your position. Examples include the sound of [...]
Light travels through air at about 186,000 miles every second. Sound, however, is much slower. A sound wave travels through the air as vibrating molecules bump into their neighbors, transferring energy. This process takes time, so a sound wave moves about 1,000 feet in that same second (the speed varies a bit, depending on temperature [...]
Picture a green leaf on a sunny day. Why does the leaf look green? When sunlight strikes the leaf, molecules inside the leaf absorb some of the energy of the light. Some wavelengths are absorbed more than others. This is the source of energy that a plant needs in order to grow. The wavelengths of [...]
Mirages occur when a sharp boundary forms between two layers of air with different temperatures. If the air just above the ground is much warmer than the air above it, light bends upward. The puddle that you see on the road ahead is actually light from the blue sky and clouds in the distance. Your [...]
The apparent bend in the spoon’s stem comes from this change in light speed as the light travels between the water and the air. You see the spoon because rays of light are reflected from its surface. When these rays of light pass from the water into the air, they travel at a different speed.
When [...]
Light travels in waves of different lengths. The wavelengths of visible light are very short—about one ten-thousandth to one one-thousandth of a millimeter. The longest waves in the familiar spectrum of visible light are red and the shortest are violet. The sun produces light across the entire span of the spectrum. When all of the [...]
In direct current (DC), electrons flow from one place to another in a single direction. For example, when you turn on a flashlight, electrons flow from the negative pole of the battery, through the light bulb, and then to the positive terminal. As they pass through the bulb, the electrons lose energy and light is [...]
Specifically, the laws of thermodynamics say that there is no way for you to get something for nothing. So, if you make one place cooler, you have to make another place warmer. As you cool your perishable foods, you heat up the kitchen. A refrigerator is a kind of heat pump. It
removes heat from the [...]
Remember, due to inertia, a moving object continues moving in a straight line unlessa force acts on it. There is a force that acts on every object near Earth—the force of gravity. If you throw a ball, it does not continue moving indefinitely in a straight line because gravity causes it to move toward the [...]
When you get into a roller coaster that loops upside down, the attendant makes sure that your safety belt or safety bar is in place. These devices are not what keeps you in place, though. Physics takes care of that.
Acceleration is a change in direction or speed. When something moves in a circle, it is [...]
