The first chapter XI colorful material world
I. Universe and microcosm
Universe → Galaxy → Solar System → Earth
Matter consists of molecules; Molecules are particles that maintain the original properties of matter; The general size is only tens of billions of meters (0.3-0.4nm).
Properties of three states of matter:
Solid: molecules are arranged closely, and there is a strong force between particles. Solids have a certain shape and volume.
Liquid: molecules have no fixed position and move freely, and the force between particles is smaller than that of solids; Liquid has no fixed shape and fluidity.
Gas: Molecules are extremely dispersed, with large spacing, and move in all directions at high speed. The interaction between particles is weak and easy to be compressed. Gas has fluidity.
Molecules are composed of atoms, atoms are composed of nuclei and (extra-nuclear) electrons (similar to the solar system), and nuclei are composed of protons and neutrons.
Nanotechnology: (1 nm = 10 nm), nanotechnology: (0. 1- 100 nm). The object of study is a small pile of molecules or a single atom or molecule.
Second, quality.
Mass: How much matter does an object contain? Mass is an attribute of the object itself, and its size has nothing to do with shape, state, position, temperature, etc. Symbol of physical quantity: m.
Units: kilograms, tons, grams and milligrams.
1t= 103kg， 1kg= 103g， 1g= 103mg。
Balance: 1, principle: lever principle.
2. Precautions: The measured object cannot exceed the weighing of the balance; Use tweezers to add and subtract weights on the plate, and the weights should not be dirty or wet; Wet objects and chemicals cannot be placed directly on the plate of the balance.
3. Use: (1) Put the balance on a horizontal platform; (2) Put the traveling code on the ruler on the left zero line, and adjust the balance nut on the beam to balance the balance (the pointer points to the center line of the reticle or the swing amplitude is equal from left to right). (3) Put the object on the left board, put the weight on the right board, increase or decrease the weight and adjust the stroke code to balance the balance. (4) Reading: the total weight plus the scale value corresponding to the travel code.
Note: In weightlessness (such as a spaceship), you can't weigh the mass with a balance.
Third, density.
Density is a special property of matter; The mass of the same substance is directly proportional to its volume, and the ratio of mass to volume is constant.
Density: The mass per unit volume of a substance is called the density of this substance.
Density is related to the kind and state of matter, affected by temperature, and has nothing to do with mass and volume.
Formula:
Unit: kg/m3 g/cm3/kloc-0 /×103kg/m3 =1g/cm3.
1L = 1dm 3 = 10-3 m3； 1 ml = 1 cm3 = 10-3L = 10-6 cubic meters.
Fourth, measure the density of matter.
Experimental principle:
Experimental equipment: balance, measuring cylinder, beaker, thin thread.
Measuring cylinder: measures the volume of liquid (which can indirectly measure the volume of solid), and the reading is based on the lowest point of concave liquid level.
Measuring the density of solids (the density is greater than water):
1. Weigh the mass m of solids with a balance; 2. Pour a proper amount of water into the measuring cylinder (which can immerse the object without exceeding the maximum scale) and read the volume of water (v1); 3. Tie the object with thin thread, put it into the measuring cylinder, and read out the total volume V2.
Note: If the density of solid is lower than that of water, needle pressing method and drop hammer method can be used.
Measure the density of liquid: Step: 1. Weigh the total mass of beaker and liquid with a balance M 1; 2. Pour the liquid in the beaker into a part of the measuring cylinder and read out the volume v2 of the liquid; 3. Weigh the mass m2 of the remaining liquid and beaker with a balance.
V. Density and social life
Density is the basic attribute (characteristic) of matter, and each matter has its own density.
Density and temperature: temperature can change the density of matter; The thermal expansion of gas is the most significant, and its density is most affected by temperature. Solids and liquids are less affected by temperature.
Abnormal expansion of water: the highest density is at 4℃; Water gets bigger when it freezes.
Density application: 1, identification of substances (density measurement) 2, calculation of mass 3, calculation of volume.
Chapter XII Movement and Strength
Description of movement
Motion is a universal phenomenon in the universe.
Mechanical motion: the change of object position is called mechanical motion.
Reference: An object selected as a standard (or an object assumed to be stationary) is called a reference.
Relativity between motion and stillness: whether the same object is moving or still depends on the selected reference object.
Second, the speed of movement.
Speed: describes the speed at which an object moves. Speed is equal to the distance traveled by a moving object in unit time.
Formula:
The unit of speed is: m/s; Kilometers per hour.
Uniform linear motion: to move at a uniform speed along a straight line. This is the simplest mechanical movement.
Variable speed motion: the speed of motion of an object is variable.
Average speed: In variable-speed movement, the speed of an object within this distance can be obtained by dividing the total distance by the time spent, which is the average speed.
Third, the measurement of time and length.
Time measuring tool: clock. Stopwatch (for laboratory use)
Unit: s minimum h
Measuring tool of length: ruler.
Unit of length: meter kilometer mark centimeter millimeter micron nautical mile
Correct use of scale;