Knowledge points of the second volume of physics in the second day of junior high school of Jiangsu Education Edition
Knowledge carding
1. Quality:
⑴ Definition: The amount of substance contained in an object is called mass.
⑵ Unit: international system unit kg, commonly used unit: t g mg.
Perceptual understanding of quality: a pin is about 80mg, and an apple is about150g.
An elephant is about 6t and a chicken is about 2kg.
⑶ Understanding of mass: The mass of a solid does not change with the shape, state, position and temperature of the object, so the mass is the inherent property of the object.
(4) Measurement:
① Measuring tools commonly used in daily life: bench scale, bench scale, bar scale and pallet scale commonly used in the laboratory. You can also measure the weight of an object with a spring dynamometer, and then calculate the weight of the object with the formula m = g/g..
(2) How to use the pallet balance: 24 words: on the horizontal platform, the traveling code is zero, the beam is balanced, the left thing is right, the first one is big, the second one is small, and the beam is balanced. Details are as follows:
A. "Look": Observe the weighing of the balance and the dividing value of the walking code on the scale.
B "release": put the balance on a horizontal platform, and put the stray code on the zero scale line at the left end of the balance.
C. "Adjustment": Adjust the balance nut at the right end of the balance beam so that the pointer points to the center line of the reticle, and then the beam is balanced.
D. "Weighing": put the measured object in the left plate, add and subtract weights in the right plate with tweezers, and adjust the position of wandering code on the scale until the light beam is balanced.
E "Note": the mass of the measured object = the total mass of the weight in the plate+the calibration value of the traveling code on the scale.
F. note: a cannot exceed the weight of the balance.
Keep the balance dry and clean.
③ Methods: A. Direct measurement: solid mass method B. Special measurement: liquid mass method and micro mass method.
Too large and too small: when the pointer is biased to the left of the dial, the measured value is greater than the real value, and when the pointer is biased to the right of the dial, the measured value is less than the real value;
Weight wear, the measured value is greater than the real value; The weight is stained with oil or other small objects, and the measured value is less than the true value.
When the stray code does not move to the 0 scale, the measured value is greater than the real value, and the larger value is the reading of the stray code.
2. Density: xkb 1.com
⑴ Definition: The mass per unit volume of a substance is called the density of this substance.
(2) Formula:
⑶ Unit: international unit kg/m3, commonly used unit g/cm3. Compare these two units: the unit of g/cm3 is larger. Unit conversion relationship:1g/cm3 =103kg/m31kg/m3 =10-3g/cm3. The density of water is 1.0× 103kg/m3, and the physical meaning is: 1.0× 103kg of water.
(4) Understand the density formula:
(1) same substance, same substance, ρ constant (m is proportional to v);
② The density ρ of an object has nothing to do with its mass, volume and shape, but is related to the mass-volume ratio;
③ When different substances have the same mass, the larger the volume, the smaller the density;
④ When different substances have the same volume, the greater the mass, the greater the density.
5] Density changes with the change of temperature, pressure and state. The density of different substances is generally different, so density is a characteristic of substances.
[6] picture: as shown on the left: ρ a >; ρ b
Once the volume measurement-measuring cylinder (measuring cup)
Usage: Measuring liquid volume (indirectly measuring solid volume).
② Usage:
"Look": unit: milliliter (ml)= centimeter 3 (cm3); Scope; Split value.
"Put": put on a horizontal platform.
"Reading": The water surface in the measuring cylinder is concave. When reading, the line of sight should be flush with the concave bottom.
Measuring the density of solids:
① principle: principle: ρ=m/v
② Method: A. Measure the solid mass m with a balance.
A. Pour a proper amount of water into a measuring cylinder and read the volume of v 1;
B, tying the object with a thin thread, immersing the object in a measuring cylinder, and reading the total volume v2;
D, obtaining the solid density rho = m/(v2-v1).
Note: When measuring irregular solid volume, drainage method can also be used, and a scientific method equivalent substitution method is adopted here. Conventional solid volume can be measured with a scale)
Levies liquid density measurement:
① principle: ρ=m/v
② Methods: A. Measure the total mass of liquid and beaker with a balance M 1;
B, pouring the liquid in the beaker into a part of the measuring cylinder, and reading the volume v of the liquid in the measuring cylinder;
C, weighing the mass m2 of the beaker and the residual liquid in the cup;
D, the density of the obtained liquid rho = (m1-m2)/v.
⑽ Application of density:
Identification of substances: density is one of the characteristics of substances, and the density of different substances is generally different, so it can be used to identify substances.
② Finding the mass: Due to the limitation of conditions, the volume of some objects is easy to measure, but it is not convenient to measure the mass. Calculate its mass with the formula m = ρ v. ..
③ Calculation of volume: Due to the limitation of conditions, the mass of some objects is easy to measure but inconvenient to measure. Calculate its volume with the formula V=m/ρ.
(4) determining the hollow solid:
Chapter 7 From Particles to the Universe
Knowledge carding
1. molecular Xkb 1.com
(1) Matter consists of molecules. If the molecule is spherical, its diameter is 10- 10m.
The molecules of all objects are constantly moving irregularly.
① Diffusion: The phenomenon that different substances enter each other when they contact each other.
② Diffusion phenomenon indicates that there are gaps between molecules A.. Molecular B is doing irregular movements.
③ Solid, liquid and gas can diffuse, and the diffusion speed is related to temperature.
④ It is necessary to distinguish between molecular motion and object motion: diffusion and evaporation are the result of molecular motion, while the convection of flying dust, liquid and gas is the result of object motion.
(3) There is interaction between attractive and repulsive molecules.
① When intermolecular distance d = intermolecular equilibrium distance r, attraction = repulsion.
(2) when d < r, when gravity plays a major role, gravity > repulsion, and gravity plays a major role. Solids are hard to break, pens write, and glue sticks to things because the attraction between molecules plays a major role.
④ When d > 10r, the intermolecular force is very weak and can be ignored.
The reason why broken mirrors can't be reassembled is that the distance between mirror blocks is much larger than the range of intermolecular force, and the mirrors can't be assembled together because of intermolecular force.
2. expenses
⑴ charged (charged): When the rubbed object has the property of attracting light and small objects, we say that the object is charged.
Light and small objects refer to pieces of paper, hair, grass balls, dust, light balls and so on.
(2) Method of charging objects:
② Contact electrification: contact electrification between an object and a charged body. If the charged body touches the electroscope metal ball, it will be charged.
③ Inductive charging: Due to the action of the charged body, the objects near the charged body are charged.
(3) Two kinds of charges:
Positive charge: regulation: the electricity carried by a glass rod rubbed with silk.
Essence: matter loses electrons.
Negative charge: regulation: the electricity carried by fur rubbing rubber rod.
Essence: matter gains extra electrons.
(4) the law of charge interaction: the same kind of charges repel each other, and the different kinds of charges attract each other.
(7) Electric neutrality: the phenomenon that the same amount of heterogeneous charges completely cancel out.
Chapter VIII Force
Knowledge carding
1. force
⑴ Concept of force: Force is the action of objects on objects.
⑵ Conditions for force generation: ① There must be two or more objects. ② There must be interaction (no contact) between objects.
⑶ Nature of force: The forces between objects are mutual (in any case, the mutual forces are equal in size and opposite in direction, and act on different objects). When two objects interact, the force applying object is also a force applying object, and vice versa.
(4) Function of force: Force can change the motion state of an object. Force can change the shape of an object.
Note: Whether the motion state of an object changes generally refers to whether the speed of the object's motion changes (the change of speed) and whether the direction of the object's motion changes.
Unit of force: the unit of force in the international system of units is Newton, abbreviated as cow, and represented by n.
Perceptual knowledge of force: the force used to take two eggs is about1n.
[6] Force measurement:
① Dynamometer: spring dynamometer.
② Spring dynamometer:
A. Principle: In a certain range, the elongation of the spring is directly proportional to the pulling force.
B. how to use it:
"Selection": Know the range and dividing value of the spring dynamometer;
"Adjustment": put the spring dynamometer in the required position, no matter whether the pointer points to zero or not, it is not in calibration;
"Measurement": The stress direction of the spring dynamometer is along the axis of the spring.
(7) Three elements of force: the magnitude, direction and action point of force.
⑻ Representation of force: Schematic diagram of force: The magnitude, direction and action point of force are represented by line segments with arrows. If there is no order of magnitude, it does not mean that the greater the force, the longer the line segment in the same picture should be.
Step 2 be flexible
(1) Elastic deformation: the property that an object is deformed by a force and returns to its original state after losing the force, which is called elastic deformation.
⑵ Elasticity: The force on an object due to elastic deformation is called elasticity.
3. Gravity:
(1) The concept of gravity: the force that an object close to the ground receives due to the gravity of the earth is called gravity. The object of gravity is the earth.
2 the formula for calculating gravity is G=mg, where g=9.8N/kg, that is to say, the gravity of an object with a mass of 1kg is 9.8N. ..
(3) Gravity direction: vertically downward. Its application is to check whether the wall is vertical and the surface is horizontal with a vertical line and a level.
(4) Center of gravity-center of gravity:
The point where gravity acts on an object is called the center of gravity. The center of gravity of an object with uniform texture and regular shape is at its geometric center.
If the center of gravity of a uniform thin rod is at its midpoint, the center of gravity of the ball is at the center of the ball.
☆ What will happen if gravity is lost: (Only two things that may happen in life are needed)
(1) The thrown object will not fall; (2) Water will not flow from high to low; (3) liquid and atmosphere will not produce pressure;
4. Friction:
⑴ Definition: When two objects in contact with each other are about to move or have moved relative to each other, a force will be generated on the contact surface, which is called friction.
(2) Classification:
(3) Direction of friction: The direction of friction is opposite to the direction of relative motion of objects, sometimes acting as resistance and sometimes as power.
(4) Static friction should be obtained through force analysis and two-force balance.
5] Under the same conditions (contact surface pressure and roughness are the same), rolling friction is much smaller than sliding friction.
[6] Sliding friction:
① measurement principle: two-force balance condition
② Measurement method: Put the wood block on a horizontal long board, and pull the wood block horizontally with a spring dynamometer to make the wood block move at a uniform speed. Read that the tension at this time is equal to the sliding friction.
Conclusion: When the roughness of contact surface is the same, the greater the pressure, the greater the sliding friction.
Under the same pressure, the rougher the contact surface, the greater the sliding friction.
In this study, the control variable method is used. The first two conclusions can be summarized as follows: the magnitude of sliding friction is related to the magnitude of pressure and the roughness of contact surface.
5. Application:
⑴ The methods to increase friction are: increasing pressure, roughening contact surface and changing rolling into sliding.
⑵ The methods to reduce friction are: reducing pressure, making contact surfaces smooth, changing sliding into rolling (rolling bearing), and separating contact surfaces from each other (adding lubricating oil, air cushion and magnetic levitation).
Chapter IX Force and Movement
Knowledge carding
1. Two kinds of power balance:
⑴ Definition: When an object is acted by two forces, it is said that the two forces are balanced if it can maintain a static state or a state of uniform linear motion.
⑵ Equilibrium conditions of two forces: two forces act on the same object, with equal magnitude and opposite directions, and the two forces are in a straight line.
Summary: The conditions of the balance of the two forces can be summarized as "one, equality, opposition and one" in four words.
(3) Comparison of balance force and interaction force:
Similarities: ① Equal in size ② Opposite in direction ③ Acting on a straight line.
Difference: the balance force acting on the object can be different forces; The interaction forces acting on different objects are forces of the same nature.
(4) the relationship between force and motion state:
The force of the object, the description of the motion state of the object.
unbalanced force
The resultant force is 0.
equilibrium state
Smooth and uniform motion
Force is not the cause of exercise.
The resultant force of unbalanced forces is not zero.
Motion state change
Change the speed and direction of movement.
Force is the reason to change the motion state of an object.
2. Galileo inclined plane experiment;
The purpose of the three experiments is to ensure that the car starts to move along the plane at the same speed.
⑵ Experimental conclusion: Under the same conditions, the more stable the plane is, the farther the car will go.
(3) Galileo's inference is that in an ideal situation, if the surface is absolutely smooth, the object will always move at a constant speed.
⑷ The excellence of Gaglio's inclined plane experiment lies not in the experiment itself, but in the unique method used in the experiment-idealized reasoning based on the experiment. It marks the real beginning of physics.
3. Newton's first law:
(1) Newton summed up the research results of Galileo, Descartes and others, and obtained Newton's first law, the content of which is that all objects always keep still or move in a straight line at a constant speed when they are not affected by external forces.
(2) Description:
A Newton's first law is generalized through further reasoning on the basis of a large number of empirical facts and has stood the test of practice, so it has become one of the basic laws of mechanics recognized by everyone. But there can't be no pressure around us, so it's impossible to prove Newton's first law directly through experiments.
B. the connotation of Newton's first law: when an object is not stressed, the original static object will remain in a static state, and the original moving object will move in a straight line at a uniform speed no matter what it does.
C. Newton's first law tells us that an object can move in a straight line at a uniform speed without force, that is, force has nothing to do with the state of motion, so force is not the reason for producing or maintaining motion.
4. inertia:
⑴ Definition: The property that an object keeps its state of motion unchanged is called inertia.
⑵ Description: Inertia is an attribute of an object. All objects have inertia under any circumstances, and the size of inertia is only related to the mass of the object, and has nothing to do with whether the object is stressed, whether it is stressed, whether it is moving or not, and the speed of movement.
☆ Sometimes people want to use inertia, and sometimes they want to prevent the harm caused by inertia. Please illustrate the above two points with examples (no need to explain).
A: utilization: run-up of long jumpers; Hard work can throw stones far away; A few pedals will make the bike slide. Precautions: Passengers in the front row of minibus should wear seat belts; Keep a distance when the vehicle is driving; Packaging glass products should be padded with thick foam plastic.
5. Force is the reason to change the motion state of an object:
(1) The change of the motion state of an object is determined by the force on the object.
⑵ Judge the stress of an object by the change of its motion state.
Chapter 10 Pressure and Buoyancy
Knowledge carding
1. Pressure:
⑴ Definition: The force acting vertically on the surface of an object is called pressure.
(2) Pressure is not always caused by gravity. Generally, when an object is placed on a horizontal plane and the vertical direction of the object is not affected by other forces, the pressure F = the gravity g of the object.
(3) The object with the weight of g is still on the bearing surface. Point out the pressure under the following conditions.
G G F+G G–F F-G F
2. Experimental study on the factors affecting the pressure effect:
(1) Description of A and B: When the stress area is the same, the greater the pressure, the more obvious the pressure effect.
(2) B and C indicate that when the pressure is the same, the smaller the stress area is, the more obvious the pressure effect is.
⑶ The conclusion of these two experiments is that the effect of pressure is related to pressure and stress area. In this experiment, the control variable method and contrast method are used to study this problem.
3. Solid pressure: xkb 1.com
⑴ Definition: The pressure per unit area of an object is called pressure.
⑵ Physical meaning: Pressure is a physical quantity indicating the action of pressure.
⑶ Formula p=F/S, where the unit of each quantity is: pressure p: Pascal (Pa); Pressure f: Newton (n);
Stress area s: m2 (square meter).
☆ When using this formula to calculate pressure, the key is to find out the pressure f (generally F=G=mg) and the stress area s (the stress area should pay attention to the contact part of two objects).
⑷ Understanding of pressure unit Pa: When a newspaper is laid flat, the pressure on the desk is about 0.5 Pa, and the pressure of a book on the desktop is about 50 Pa; When an adult stands, the ground pressure is about1.5×104 pa; It shows that when people stand, the pressure on their feet per square meter is:1.5×104 n.
5] Application:
(1) under the condition of constant pressure, we can reduce the pressure by increasing the stress area, such as laying sleepers on the rails, installing crawler on the tanks and making the schoolbags wider.
② You can also increase the pressure by reducing the stress area, such as sewing the needle very thin and the blade of the kitchen knife very thin.
4. Liquid pressure
⑴ Reasons for pressure inside liquid: Liquid is gravity and has fluidity.
⑵ Measuring tool: pressure gauge Purpose: To measure the pressure inside the liquid.
(3) the law of liquid pressure:
(1) The liquid has pressure on the bottom of the container and the measuring wall, and the liquid has pressure in all directions;
② At the same depth, the pressure of liquid in all directions is equal;
③ The pressure of liquid increases with the increase of depth;
④ The pressure of different liquids is related to the density of liquids.
5. Atmospheric pressure
⑴ Concept: The pressure of the atmosphere on the object immersed in it is called atmospheric pressure, which is generally expressed by P0. Note: There is a difference between "atmospheric pressure" and "barometric pressure" (or partial pressure). For example, the barometric pressure in a pressure cooker refers to partial pressure. The pressure cooker is called atmospheric pressure.
⑵ Cause: Because the air is affected by gravity, it has fluidity.
(3) the existence of atmospheric pressure-experiments prove that:
A famous experiment in history —— the hemispheric experiment in Madeborg.
Small experiments-the experiment of covering a cup, the experiment of swallowing eggs in a bottle, and the sucker.
⑷ Experimental measurement of atmospheric pressure: Torricelli experiment.
① Experimental process: Fill a glass tube with a length of about 1m and one end closed with mercury, plug the nozzle, then insert it backwards in the mercury tank, and loosen the fingers blocking the nozzle. After the mercury level in the tube drops a little, it will not drop. At this time, the height difference of mercury column inside and outside the tube is about 76 cm.
(2) Principle analysis: Take a liquid film inside the pipe at the level of the liquid level outside the pipe. Because the liquid is immobile, the liquid film is balanced by the upper and lower pressures. That is, upward atmospheric pressure = pressure generated by mercury column.
③ Conclusion: The atmospheric pressure P0 = 76 cmhg =1.0×105 Pa (the mercury column height difference changes with the change of external atmospheric pressure).
④ Description:
A. The purpose of filling the glass tube with mercury before the experiment is: after the glass tube is inverted, there is vacuum above the mercury; If it is not filled, the measurement result is very small.
B if mercury is replaced by water in this experiment, the length of the glass tube is about10 m.
C, gently lift or hold down the glass tube, keep the height difference between the inside and outside of the tube unchanged, tilt the glass tube, keep the height unchanged, and lengthen the length.
D standard atmospheric pressure: the atmospheric pressure supporting 76 cm Hg is called standard atmospheric pressure.
A standard atmospheric pressure is 1 .× 105 Pa (76 cm Hg).
6. Characteristics of atmospheric pressure:
⑴ Features: There is pressure in all directions in the air, and the atmospheric pressure at a certain point in the air is equal in all directions. The air pressure decreases with the increase of altitude, and the value of air pressure is related to the change of location, weather and season.
Generally speaking, the air pressure in sunny days is higher than that in cloudy days, and it is higher in winter than in summer.
⑵ Study on the variation law of atmospheric pressure: within 2000m above sea level, the atmospheric pressure will decrease by 100 Pa( 1mmHg) for every increase of 10m.
⑶ Measuring tool: The instrument for measuring atmospheric pressure is called barometer. Mercury barometer and aneroid barometer
⑷ Application: Piston pump and centrifugal pump.
5] Boiling point and pressure:
Content: The boiling points of all liquids decrease when the air pressure decreases and increase when the air pressure increases.
Application: pressure cooker, water removal.
[6] Gas partial pressure: (gas volume, gas temperature, gas molecular number, etc. )
When the temperature of a certain mass of gas is constant, the smaller the gas volume, the greater the pressure, and the larger the gas volume, the smaller the pressure.
(7) Application of atmospheric pressure: (☆ Give some examples of applying atmospheric pressure knowledge in your daily life? )
Answer: ① use a plastic straw to suck drinks from the bottle; ② Draw water for pens; ③ Use clothes hangers with suction cups; ④ Centrifugal water pump.
7. buoyancy
⑴ Definition: All objects immersed in liquid (gas) are subjected to the vertical upward force of liquid (gas), which is called buoyancy.
⑵ Buoyancy direction: vertical upward, and the object of force is liquid (gas).
(3) Causes of buoyancy (essence): The upward pressure of liquid (gas) on an object is greater than the downward pressure, and the difference between the upper and lower pressures is buoyancy.
8. Archimedes principle:
(1) Content: An object immersed in a liquid is subjected to upward buoyancy, and the buoyancy is equal to the gravity when it displaces the liquid.
(2) Formula: f float = G row = ρ liquid v row g It can be seen from the formula that the buoyancy of liquid to an object is related to the density of liquid and the volume of liquid displaced by the object, but has nothing to do with the mass, volume, gravity, shape and immersion depth of the object.
(3) Applicable conditions: liquid (or gas)
9. The ups and downs of objects:
(1) Prerequisite: The object is immersed in liquid and only subjected to buoyancy and gravity.
② Please complete blanking according to the schematic diagram.
Sink, float, float, float
F float < G F float = G F float > G F float = G.
ρ liquid ρ substance ρ liquid > ρ substance
③ Description:
A. An object with uniform density is suspended (or floated) in a liquid without changing its ups and downs after cutting a piece. If an object is cut into two pieces with different sizes, both the big piece and the small piece are suspended (or floating).
B. An object floats in a liquid with a density of ρ. If the exposed volume is 1/3 of the total volume of the object, the density of the object is
Analysis: So:
C. Comparison between suspension and floating
Same: f float = G different: suspended ρ liquid = ρ substance; Line v = object v
Floating rho liquid