Eight physics knowledge points textbook version .

Physics knowledge points are not memorized, but understood.

1. The propagation of sound requires a medium; Solids, liquids, and gases can all transmit sound; Sound travels with the least loss in solids (farthest in solids, railroad tracks), and in general, sound travels fastest in solids and the slowest in gases (except for cork);

2. Vacuum cannot transmit sound, and astronauts on the moon (in space) can only talk wirelessly;

3. Sound propagates in the form of waves (sound waves);

Note: The sound object must vibrate, and the sound may not be heard if there is vibration;

4. Speed of sound: the distance that an object travels in per second is called the speed of sound, and the unit is m s; The formula for calculating the speed of sound is v=s t; The velocity of sound in air is 340m s;

Mask: Plane Mirror: Imaging Features:

Equal size, equal distance, vertical, virtual image, object size equal; The distance between the image and the object and the mirror surface is equal; The connection line of the image and object is perpendicular to the mirror; The image of an object in a flat mirror is a virtual image. Imaging principle: the reflection theorem of light; Real and imaginary:

Real image: The image of the actual confluence point of light: The image of the converging point of the reverse extension of the reflected light.

Spherical Mirror: Definition: The inner surface of a spherical surface is used as a reflective surface. Properties: A concave mirror can concentrate parallel rays of light towards it at one point.

Noise refers to the sound emitted by the sound emitter doing irregular and chaotic vibrations; Angular noise in environmental protection refers to the sound that interferes with people's normal rest, study and work, and the sound that interferes with the sound that people want to hear.

People use decibels (dB) to classify sounds; 0db: The faintest sound a person can just hear. Hearing protection: <90db. Guaranteed work-study: <70db. Guaranteed rest and sleep: <50db.

Methods of noise attenuation: attenuation at the sound source, attenuation during propagation, attenuation at the human ear. Examples are the sound source (to prevent the generation) of the muffler of the exhaust pipe (to hinder the propagation), the soundproof dragon, the vacuum glass window at the human ear (to prevent the in-ear), the earplugs, and the earmuffs.

The above is the physics knowledge points I have summarized for you in the first volume of the eighth grade, I hope it will be helpful for junior high school students to learn physics!

1. The propagation of light can shine and is called a light source, and the moon is not the sun. The propagation of light is conditional, and the homogeneous medium is straight.

2. The reflection of light The normal passes through the incident point, and the dotted line reflects perpendicular to the surface. The reflected incidence is on both sides, and the reverse angle of entry is always equal. The angle included in the method is the entry angle, and the entry angle increases and the reverse angle increases. All objects are reflected, specular reflection diffuses the opposite side.

3. Plane mirror imaging Plane mirror, into a virtual image, the size is equal and symmetrical. The image of the object to the mirror distance is trapped, etc., they are connected to the mirror surface. The reflection of the graph is inversely extended, and the intersection point of the dashed line is the image point. All image points form an image, and the virtual image should be represented by a virtual image.

4. Refraction of light Light enters from one object to another, and reverses and refractions occur at the same time. The diagonal line is close to the water to be refracted, and the polyline is close to the normal. The normal is perpendicular to the interface, and the polyline incoming line is divided into two sides.

The light in the water obliquely enters the air, the broken line is far from the normal, the trees become taller underwater, and the fish become shallower on the shore.

5. The dispersion of light, red, orange, yellow, green, blue, indigo, violet, white light, dispersion of seven colors. The color light is red, green and blue, and the pigment is red, blue and yellow. Red objects reflect red light, and other colors of light are absorbed. There is no reflected light into the eye, and one piece is black.