First, the length measurement
1, length measurement
The measurement of length is the most basic measurement, and the most commonly used tool is the scale.
2, the length of the unit and conversion
The international unit of length is meter (m), and commonly used units are kilometer (Km), decimeter (dm), centimeter (cm), millimeter (mm), micron (um) and nanometer (nm).
1km 103m 10m 10dm 10cm 10mm 103um 103nm
When the length is converted to units, the small units are multiplied and the large units are divided by the small units.
3. Correct use of the scale
(1) Pay attention to the zero scale line, measuring range and dividing value before use.
(2) Pay attention when using
(1) The ruler should be placed along the measured length, and the edge of the ruler should be aligned with the measured object. It must be placed in a straight line and cannot be skewed.
② Don't use worn zero scale lines. If another whole scale line is used as the zero scale line due to the wear of the zero scale line, don't forget to subtract the scale value of the replacement zero scale line from the final reading.
③ The thick ruler should be placed vertically.
(4) When reading, the line of sight should be perpendicular to the ruler.
4. Record the measured values correctly
The measurement results consist of numbers and units.
(1) It is meaningless to write numbers without units.
(2) When reading, you need to estimate the next digit of the scale value.
Step 5 be wrong
The difference between the measured value and the true value
Errors are inevitable, but they can be minimized. Avoidable mistakes should not happen.
The basic method to reduce the error is to measure the average for many times. In addition, selecting precision instruments and improving measurement methods can also reduce the error.
6, special method measurement
(1) accumulation method
For example, measuring the diameter of metal wire or the thickness of paper.
(2) Caliper method
(3) substitution method
Second, simple exercise.
1, mechanical motion
The change of the position of an object is called mechanical motion.
All objects are in motion, and there is no absolutely stationary object, which means that motion is absolute. We usually say that motion and static are relative to another object (reference), so the description of motion is relative.
2. Reference object
When studying mechanical motion, the object chosen as the standard is called the reference object.
(1) Not all reference objects are stationary relative to the ground. Just choose which object as the reference, and we assume that the object is stationary.
(2) Reference objects can be selected arbitrarily, but different reference objects may describe the same object motion differently.
3. Relatively static
Two objects moving in the same direction at the same speed, or the position between them remains the same, are relatively static.
4, uniform linear motion
Uniform linear motion is called uniform linear motion.
Uniform linear motion is the simplest mechanical motion.
5. Speed
(1) speed is a physical quantity representing the speed of an object.
(2) In uniform linear motion, the speed is equal to the distance traveled by the moving object in unit time.
(3) speed formula: v= S t
(4) the unit of speed
International unit: m/s Common unit: km/h1m/s = 3.6 km/h.
6. Average speed
The ratio of the time required for a variable-speed object to pass a certain distance is called the average speed of the object at that distance.
Leveling speed must indicate the average speed of distance or time.
7. Measure the average speed
Principle: v = s/t
Measuring tools: scales, stopwatches (or other timers)
Third, sound phenomenon.
1, the appearance of sound
Everything that makes a sound vibrates. When the vibration stops, the sound will also stop.
Sound space is produced by the vibration of objects, but not all vibrations will produce sound space.
2. Transmission between voices
The transmission of sound needs medium, and vacuum cannot transmit sound.
(1) Sound is transmitted by all gases, liquids and solids, which are called media. Even if astronauts on the moon talk face to face, they still need to rely on radio. That's because there is no air on the moon, and vacuum can't spread sound.
(2) Sound travels at different speeds in different media.
Step 3 echo
In the process of sound propagation, the sound that people hear again when they encounter obstacles is called echo.
(1) Conditions for distinguishing echo from original sound: the echo reaches the human ear more than 0. 1 second later than the original sound.
(2) When it is less than 0. 1 sec, the reflected sound can only strengthen the original sound.
(3) Echo can be used to measure the depth of the sea or how far the probe is from obstacles.
4. Tone
The sound level is called tone, which is determined by the vibration frequency of the speaker. The higher the frequency, the higher the pitch.
Step 5: Volume
The volume of sound is called loudness, which is related to the amplitude of speaker vibration and the distance from the sound source to the human ear.
6, timbre
The quality of sound produced by different vocal bodies is called timbre.
7. Noise and its sources
From the physical point of view, noise refers to the sound produced when the vocal body vibrates irregularly and disorderly. From the perspective of environmental protection, all sounds that hinder people from resting, studying and working normally belong to noise.
8, the division of sound level
People use decibels to divide sound levels. 30 dB -40 dB is an ideal quiet environment. If it exceeds 50dB, it will affect sleep. If it exceeds 70dB, it will interfere with the call and affect the work efficiency. If you live in a noise environment above 90dB for a long time, it will affect your hearing.
9. Ways to reduce noise
Can be attenuated at the sound source, during propagation and at the human ear.
Fourth, thermal phenomenon.
1, temperature
The degree of heat and cold of an object is called temperature.
2. Celsius temperature
The temperature of ice-water mixture is defined as 0 degrees, and the temperature of boiling water at 1 standard atmospheric pressure is defined as 100 degrees.
3. Thermometer
Principle (1): liquid expands when heated and contracts when cooled.
(2) Structure: glass shell, capillary, glass bubble, scale and liquid.
(3) Use: Before using the thermometer, pay attention to the measuring range and recognize the dividing value.
Do the following three things with a thermometer.
① The thermometer is in full contact with the measured object.
(2) Wait until the figures are stable before reading.
(3) When reading, the line of sight should be flush with the upper surface of the liquid level, and the thermometer is still in close contact with the measured object.
4. The main differences between thermometers, experimental thermometers and thermometers.
A construction method of range division value
At 35-42℃, there is a contraction above the glass bulb of the thermometer, which leaves the human body for reading.
(2) It needs to be dried before use.
The experimental thermometer must be -20- 100℃, 1℃. You can't read without the measured object, and you can't throw it away.
The thermometer is not -30-50℃ 1℃.
5, melting and solidification
The change of a substance from solid to liquid is called melting, and melting requires heat absorption.
When a substance changes from liquid to solid, it is called solidification, and solidification gives off heat.
6. Melting point and freezing point
(1) solids can be divided into two types: crystalline and amorphous.
(2) Melting point: All crystals have a certain melting temperature, which is called melting point.
Freezing point: Crystals have a certain freezing temperature, which is called freezing point.
The freezing point and melting point of the same substance are the same.
7. The change of a substance from liquid to gas is called vaporization. There are two different ways of vaporization: evaporation and boiling, both of which absorb heat.
8, evaporation phenomenon
(1) Definition: Evaporation is a phenomenon that liquid can vaporize at any temperature and only occurs on the surface of liquid.
(2) Factors affecting evaporation rate: liquid temperature, liquid surface area and liquid surface air velocity.
9, boiling phenomenon
(1) Definition: Boiling is a violent vaporization phenomenon that occurs simultaneously inside and on the surface of a liquid.
(2) Conditions for liquid boiling: ① The temperature reaches the boiling point; ② Continue to absorb heat.
10, sublimation and solidification phenomenon
(1) The direct change of a substance from a solid state to a gaseous state is called sublimation, and the direct change from a gaseous state to a solid state is called sublimation.
(2) Sublimation and Sublimation in daily life (frozen wet clothes dry, frost in winter)
1 1, sublimation absorbs heat and condensation releases heat.
Verb (abbreviation for verb) light reflection
1, light source: An object that can emit light is called a light source.
2. Light propagates in a straight line in a uniform medium.
The atmosphere is uneven, and when light shines from outside the atmosphere to the ground, it will bend.
3. the speed of light
The propagation speed of light in different substances is generally different, and it is the fastest in a vacuum.
The propagation speed of light in vacuum is C = 3× 108 m/s, which is close to this speed in air, 3/4C in water and 2/3C in glass.
4. Application of linear propagation of light.
Many optical phenomena can be explained: laser collimation, shadow formation, lunar eclipse, solar eclipse, pinhole imaging and so on.
5. light
Light: a straight line indicating the direction of light propagation, that is, draw a straight line along the direction of light propagation, and draw an arrow on the straight line to indicate the direction of light propagation (light is imaginary, but actually does not exist).
6. Light reflection
When light shoots from one medium to the interface of another medium, part of the light returns to the original medium, which changes the direction of light propagation. This phenomenon is called light reflection.
7, the law of light reflection
The reflected light is on the same plane as the incident light and the normal line; Reflected light and incident light are separated on both sides of the normal; The reflection angle is equal to the incident angle.
It can be summarized as: "three lines on one side, two lines apart, and two angles are equal."
Understand:
(1) The reflected light is determined by the incident light, and the word "anti" should be used as the head in the narration.
(2) the condition of reflection: the junction of two media; Place of occurrence: incident point; Result: Return to the original media.
(3) The reflection angle increases with the increase of incident angle and decreases with the decrease of incident angle. When the incident angle is zero, the reflection angle also becomes zero.
8, two kinds of reflection phenomenon
(1) Specular reflection: parallel light rays are reflected by the interface and emitted in a certain direction in parallel, and the reflected light rays can only be received in a certain direction.
(2) Diffuse reflection: After the parallel light is reflected by the interface, it is reflected in different directions, that is, the reflected light can be received in different directions.
Note: Both specular reflection and diffuse reflection follow the law of light reflection.
9. In the reflection of light, the light path is reversible.
10, the influence of plane mirror on light.
(1) imaging (2) changing the propagation direction of light.
1 1, the characteristics of plane mirror imaging
(1) The image is an upright virtual image (2) The size of the image and the object (3) The connecting line between the image and the object is perpendicular to the mirror, and the distance between the image and the object and the mirror is equal.
Understanding: Images and objects formed by plane mirrors are symmetrical figures with the mirror surface as the axis.
12, the difference between real image and virtual image
The real image is the gathering of actual light, which can be received by the screen and of course seen by the eyes. The virtual image is not formed by the convergence of actual light, but by the intersection of opposite extension lines of actual light, which can only be seen by the eyes and not received by the screen.
13, the application of plane mirror
(1) reflection in water (2) flat mirror imaging (3) periscope
Sixth, the refraction of light.
1, light refraction
When light inclines from one medium to another, the propagation direction generally changes, which is called light refraction.
Understanding: the refraction of light occurs at the junction of two media just like the reflection of light, except that the reflected light returns to the original medium and the refracted light enters the other medium. Because the propagation speed of light in two different substances is different, the propagation direction changes at the junction of two media, which is the refraction of light.
Note: At the junction of two media, both refraction and reflection will occur.
2, the law of refraction of light
When light is obliquely incident from the air into water or other media, the refracted light is on the same plane as the incident light and the normal line, and the refracted light and the incident light are separated on both sides of the normal line; The refraction angle is smaller than the incident angle; When the incident angle increases, the refraction angle also increases; When the light is perpendicular to the surface of the medium, the propagation direction is unchanged and the refraction of the light path is reversible.
Understanding: The law of refraction is divided into three points: (1) Three lines and one face (2) Two lines are separated (3) The relationship between the two angles is divided into three situations: ① When the incident light is incident on the vertical interface, the refraction angle is equal to the incident angle is equal to 0; (2) When light is obliquely incident from air to water and other media, the refraction angle is smaller than the incident angle; (3) When light enters the air obliquely from a medium such as water, the refraction angle is greater than the incident angle.
3. The optical path is reversible in the refraction of light.
4, lens and classification
Lens: Made of transparent material (usually glass), at least one surface is a part of a spherical surface, and the thickness of the lens is much smaller than its spherical radius.
Classification: convex lens: thin edge and thick center.
Concave lens: thick edge and thin center.
5. Main optical axis, optical center, focal point and focal length
Principal optical axis: a straight line passing through two spherical centers.
Optical center: there is a special point on the main optical axis, through which the propagation direction of light remains unchanged. (The center of the lens can be considered as the optical center.)
Focus: The point at which the convex lens can converge the light parallel to the main axis on the main optical axis, which is called the focus of the lens and is represented by "F".
Virtual focus: the light parallel to the main optical axis becomes divergent after passing through the concave lens, and the backward extension line of the divergent light intersects with a point on the main optical axis, which is not the convergence point of the actual light, so it is called virtual focus.
Focal length: The distance from the focal point to the optical center is called focal length, which is indicated by "F".
Each lens has two focal points, a focal length and an optical center. draw
6. The influence of lens on light
Convex lens: convex lens (as shown in the figure)
Concave lens: it diverges light (as shown in the figure)
7, convex lens imaging law
object distance
imaging
Similar in size
Image distance between virtual image position and real image position
(5) should be used
U & gt2f reduces both sides of the real-image lens F.
U = 2f, and both sides of the large real-image lens v = 2f.
f & ltu & lt2f。 V & gt2f slide projector on both sides of magnifying real image lens
U = f is not like a picture.
U<f magnifying virtual image lens on the same side v > U magnifying glass
Oral memory method of convex lens imaging law
Oral decision 1:
"One focus is virtual reality, and the other focus is size; The same side of the virtual image is positive; The real image is reversed and the object image becomes smaller. "
Oral decision 2:
Three object distances and three boundaries, and the imaging changes with the object distance;
The reality of distant objects is small and close, and the reality of near objects is big and far.
If the object is focused, the virtual image is immediately enlarged;
Slide show is so large that the object is between one focus and two focuses;
If the camera shrinks you a little, the focal length of the object will be twice as far.
Oral decision 3:
Convex lens, high power, photography, slide show, magnification;
Double Jiao Wai is actually very small, and double coke is actually very big;
If the object is in focus, the virtual image on the same side of the object is large;
Remember a rule, birds of a feather flock together.
8. In order to make the image on the screen "vertical" (upward), the slide should be inserted backwards.
9. The lens of a camera is equivalent to a convex lens, and the film in the camera box is equivalent to a light screen. We adjust the focus ring, not the focal length, but the distance from the lens to the film. The farther the object is from the lens, the closer the film is to the lens.
Seven, quality and density
1, mass
(1) Definition: The quantity of substances contained in an object is called mass. Represented by the letter "m"
(2) Quality is an attribute of an object:
For a given object, its mass is certain and does not change with the shape and position of the object.
Settings, status and temperature changes.
(3) Unit and conversion of quality:
The main unit of mass is kilogram (kg). Commonly used units are tons (t), grams (g) and milligrams (mg).
1t103kg103g103mg.
2. Quality measurement
The tool to measure the quality of life is a scale. In the physics laboratory, scales are used to weigh the mass, including pallet scales and physical scales.
(1) How to use the balance:
(1) Put the balance on a horizontal platform, and put the stray code on the zero line at the left end of the balance.
② Adjust the balance nut at the right end of the beam so that the pointer is located at the center line of the indexing plate, and then balance the beam.
(3) Estimate the mass of the measured object, put the measured object in the left plate, add and subtract the weight in the right plate with tweezers, and adjust the wandering position on the balance until the beam is balanced.
(2) Matters needing attention in using the balance:
(1) After adjusting the balance, the left and right trays cannot be interchanged, otherwise the beam balance will be readjusted.
② The mass of the measured object cannot exceed the maximum weight.
(3) The heavy objects should be handled with care, not with hands, but with tweezers, so as to avoid the sweat on hands corroding the heavy objects.
④ Keep the balance plate dry and clean. Please do not place wet or corrosive objects directly.
(3) Weighing and sensing of balance:
The maximum mass that each balance can weigh is called the maximum weighing of the balance, which is also called weighing.
Inductance represents the minimum mass that can be measured by the balance, that is, the mass represented by the minimum scale on the balance.
3. Density
Density is a property of matter.
(1) Definition: The mass per unit volume of a substance is called density. Represented by the letter ρ.
(2) Density calculation formula:
(3) Unit: the international unit is kg/m3, and the commonly used unit in experiments is g/cm3, 1g/cm3= 103kg/m3.
Eight, force
1, the definition of force
(1) Definition: Force is the action of an object on an object.
(2) Description: The "function" in the definition is an abstract summary of specific actions such as pushing, pulling, lifting, hanging and pressing.
2. Understanding of the concept of force
When the (1) force occurs, there must be two (or more) objects, that is, without objects, there will be no powerful effect.
(2) When an object is stressed, there must be another object exerting force on it. The stressed object is called the stressed object, and the applied object is called the applied object. So the force of an object without force or an object without force does not exist.
(3) There is not necessarily a force between objects that are in contact with each other, and there is not necessarily no force between objects that are not in contact. "Contact or not" can't be used as the basis for judging whether the force occurs.
(4) The forces between objects are interactive.
(1) The action of the force-exerting object and the force-exerting object is mutual, and this pair of forces always produces and disappears at the same time.
② The object of force application and the object of force application are relative. When the object of study changes, the object of force application and the object of force application also change.
3, the role of force-from this we can judge whether there is a strong force.
(1) can change the motion state of an object. The change of motion state includes the change of motion speed and the change of motion direction
(2) It can change the shape and size of objects.
4. Units of force
In the international system of units, the unit of force is Newton, abbreviated as cow, and represented by the symbol N. The size of 1N is equivalent to the force of picking up two eggs.
5, force measurement
(1) Tool: dynamometer. The dynamometer commonly used in the laboratory is the spring scale.
(2) Principle of spring scale: The greater the tension of the spring, the longer the extension of the spring.
6, the correct use of spring scale
(1) Observe whether the measuring range, dividing value and pointer of the spring scale are on the zero line.
(2) When reading, the line of sight, pointer and scale line should be on the same horizontal plane.
7, the three elements of force
The magnitude, direction and action point of force are called the three elements of force, and they all affect the action effect.
8. Diagram of force: The three elements of force are represented by line segments with arrows.
9. Drawing method of force diagram
(1) Draw a stressed object: generally, it can be represented by a square or rectangle, and the spherical surface can be represented by a circle.
(2) Determine the action point: the action point is drawn on the stressed object, at the midpoint of the contact surface between the stressed object and the applied object. If the stressed object and the applied object are not in contact or more than two forces are applied to the same object, the point of action is drawn in the geometric center of the stressed object.
(3) Determine the scale: for example, how many newtons the line segment length 1 cm represents.
(4) Draw a line segment: draw a straight line along the direction of the force from the action point of the force according to the set scale to indicate the magnitude of the force.
(5) Direction of force: Draw an arrow at the end of the line segment to indicate the direction of force.
(6) Mark the symbol and numerical value of the graphic force near the arrow.
10, schematic diagram of force
In some cases, you only need to describe the force of an object qualitatively, and you don't need to express the force accurately, so you can draw a schematic diagram of the force.
1 1, the concept of gravity
(1) Definition: The force that an object near the ground receives due to the gravity of the earth is called gravity.
(2) Understanding: ① The object of gravity is the earth, and its force-bearing object is all objects close to the ground. ② The gravity is related to the mass of the object.
12, three elements of gravity
(1) size: G = mg
(2) direction: always vertical downward (vertical horizontal downward)
(3) point of action: the point of action of gravity is on the center of gravity of the object. The center of gravity of an object with regular shape and uniform mass distribution is in its geometric center.
13, the concept of resultant force
(1) resultant force: If one force produces the same effect as two forces acting together, this force is called the resultant force of those two forces.
(2) Understanding: ① The concept of resultant force is based on "equivalence", that is, resultant force replaces component force, so resultant force is not another force acting on an object, it just replaces the original two forces, so don't mistake the object for being acted by resultant force at the same time. (2) The condition for the combination of two forces is that these two forces must act on an object at the same time, otherwise the resultant force is meaningless.
14, force synthesis
Given the magnitude and direction of several forces, the magnitude and direction of resultant force is called resultant force.
(1) When two forces are in the same direction, the resultant force is equal to the sum of the two forces; The two forces are in the same direction.
Mathematical expression: F =F 1+F2.
(2) When the two forces are in opposite directions, the resultant force is equal to the difference between the two forces, and the direction is the direction with large force.
Mathematical expression: f = f 1-F2 (where: F 1 > F2).