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Considering the air resistance, is the falling time of different objects at the same height related to the density? As the title!
If the volume is the same, it depends on the density
How to understand the explanation of the experiment that the density of oxygen is higher than that of air,
1. A bottle of oxygen is collected by the method of exhausting air upward, and the wood bar with spark is inserted into the bottle mouth. The re ignition of the wood bar can be observed, which indicates that the density of oxygen is higher than that of air
2. Open two bottles of oxygen collected by drainage method and place them upside down for 1-2 minutes. After that, insert a piece of wood with spark into the two bottles. The one placed upside down still can't regenerate, indicating that the density of oxygen is higher than that of air
3. Keep the bottle mouth up and the bottle mouth down in the air for a period of time
Ignite the sticks with alcohol, and then extinguish them; extend the sticks with sparks into the two gas collecting bottle ports, and the sticks with the ports facing up make the sticks re ignite, indicating that O2 does not escape, so the oxygen density is higher than that of air
4. Inertia test of two balloons of equal volume under the same conditions by using inertia reasons; put two balloons equally filled with air and oxygen on the bus, and when the bus stops suddenly, the balloon filled with oxygen should go far ahead, indicating that the mass is large, so as to know that the density is larger
Law of conservation of physical and mechanical energy
The correct conditions for the conservation of mechanical energy are ()
1. If the external force on a body is zero, the mechanical energy of the body is conserved
2. The mechanical energy of an object is conserved if the total force exerted on it is zero
3. There is no work done by a body except gravity, and its mechanical energy is conserved
4. None of the above is true
The answer is d
(please explain why it's right and why it's wrong)
A conservation of mechanical energy means that other forces except gravity and spring force do not work, and if the force is balanced, the friction force is not conserved
B gravity is also an external force
C see a
RELATED INFORMATIONS
- 1. On the conservation law of physical mechanical energy The radius of the smooth track fixed in the vertical plane is r, and a small ball with mass m moves in a circle on the track in an anti clockwise direction. If the pressure of the ball on the track is 8 mg at the lowest point a, the pressure on the track is 8 mg when the ball moves to the highest point B______ The answer is 2mg, but I don't know why
- 2. Law of conservation of mechanical energy The trolley with mass m and length L stops on a smooth horizontal plane, and the small block with mass m is placed on the leftmost end of the trolley. Now, a right water balance force F is applied on the small block to make the block move uniformly and linearly from the static state. The friction force between the block and the trolley is f '. When the block slides to the rightmost end of the trolley, the distance of the trolley is s. in this process, when the block slides to the rightmost end of the trolley, the distance between the block and the trolley is s, Is the added mechanical energy of block and trolley FS? Why?
- 3. In the experiment of using free falling motion to verify the law of conservation of mechanical energy: if the instantaneous velocity is calculated and verified by measuring the distance between two points on the paper tape, the distance between point 2 and point 4 is S1, the distance between point 0 and point 3 is S2, and the period of tapping is t The relation of T = 0___ ．
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- 5. What's the difference of Ohm's law formula in AC circuit?
- 6. The formula of Ohm's law in Physics
- 7. How can Archimedes' principle be understood
- 8. What does Archimedes' principle show
- 9. Physics problems. Archimedes principle 1. The bottom area of the thin-walled cylindrical container placed on the horizontal table is 100 square centimeters. The hook of the spring dynamometer is hung with an object block of 10N. Now immerse the object block in the water, and the water surface in the container rises from 16cm to 20cm. Calculate the volume of the liquid discharged by the object block, the buoyancy of the object block, and the indication of the spring dynamometer 2. The gravity of a metal block in the air is 39n. When it is completely immersed in water, the indication of the spring dynamometer (the metal block does not contact the bottom) is 34n. Calculate the buoyancy of the metal block by water and the volume of the metal block
- 10. A hydrogen balloon, with a net weight of 30n, is filled with 20m and 179; the density of hydrogen is 0.09kg/m and that of air is 1.29kg/m;, G=10N/kg (1) How many objects can fall from the bottom of a hydrogen balloon
- 11. How to design experiments in physics to prove that air resistance affects the falling of objects?
- 12. What are the conditions of the law of conservation of momentum, the law of conservation of kinetic energy and the law of conservation of mechanical energy, What's the difference?
- 13. As for the applicable conditions of the law of conservation of mechanical energy, the correct one in the following statement is () A. When there are other external forces, as long as the combined external force is zero, the mechanical energy is conserved. C. when there are other external forces, as long as the work of the resultant force of other forces is zero, the mechanical energy is conserved. D. when the projectile flies in the air without resistance, it is only affected by the heavy force, so the mechanical energy before and after the explosion is conserved
- 14. The condition of the law of conservation of mechanical energy It is said in the book that the condition of conservation of mechanical energy is that the work is only done by gravity or elastic force. An object sliding on a smooth slope is only subject to gravity and supporting force, so its mechanical energy is conserved. However, if a crane lifts an object, its mechanical energy is not conserved, but it is only subject to gravity and tensile force. We all know that tensile force is also elastic force, so why? According to the book, the condition for the conservation of mechanical energy is that it is only affected by gravity or elastic force
- 15. The results are as follows: 1. The ball moves from point a to point B with the initial velocity V, and then returns automatically. The velocity of the ball passing through point a is () (the picture of this question is: A is on a horizontal track, moving for a period of time and then on an inclined plane, the height of the inclined plane is h, and the highest point is b) 4 options A radical (V ^ 2-4gh) B radical (4gh-v ^ 2) C radical (V ^ 2-2gh) D radical (2gh-v ^ 2)
- 16. According to the law of conservation of mechanical energy The content of the law of conservation of mechanical energy says that only gravity (or spring force) does work. Does that mean that only spring force does work, and other forces can't?
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- 20. Remainder theorem If we divide the polynomials f (x) and G (x) by 2x ^ 2-3x-2, we can get the co expressions 2x + 3 and 4x-1 respectively, then the co expressions obtained by dividing f (x) - G (x) by 2x + 1 are