Ask for junior high school physics questions, hurry! Urgent junior high school physics topics!

The speed at which objects are falling freely in the air is getting faster and faster, illustrates.

Is it true that the earth has a gravitational force on an object f=ma, that is, g=mg (principle of physics) and the internal energy of an object with a high temperature must be large? (If not, please give a counter-example) is not true. For example, the steam head of a train has a high temperature, but the internal energy does not increase with the increase in temperature, because part of the internal energy is converted into mechanical energy and released.

Relationship between rubber film tension.

Force can change the state of motion of an object.

No, 100 tons of water at 25 degrees Celsius has more internal energy than water at 30 degrees Celsius.

3.Rub the floor vigorously to make the ground relatively smooth compared to before, so that the light from the ground can be relatively parallel to the human eye, so that the original color is revealed.

1.(The principle of the piezometer is that the internal pressure of the liquid squeezes the rubber film to deform it to produce a pressure difference to change the height of the liquid level, in this process, not all energy is converted into the energy that makes the liquid level drop, and a part of the force is lost, such as squeezing the rubber film to deform it will consume energy, so) the liquid level height in the U-shaped tube of the piezometer is less than the depth of the metal box.

2.The energies are interchangeable (gravitational potential energy, kinetic energy).

4.No, 1 kg of 10 water has more internal energy than 1 g of 20 water (the internal energy is related to the state, temperature, and volume of the object).

The frictional force between AB is 0n because it moves at a uniform speed, so object A is moving by inertia and is not subject to friction.

w=fs=400*100=40000j

The magnitude of sliding friction is proportional to the magnitude of pressure, so let f(friction)=kf(pressure), then 400=500k, when f=450, f=360n, so w is useful = fs=360*100=36000j

Mechanical efficiency = 36000 40000 = 90%.

Item A refers to "the pressure of the two containers on the tabletop", that is, the gravity of the water and the container, and the landlord's method is to find the pressure of the water on the bottom of the container, which is equal, and the pressure on the table and the pressure on the container are different concepts.

For this question, choose d and b'It is conical, and after putting in the wooden block, the water rises more than A, so the landlord can find out that the pressure of water at the bottom of container B is greater than the pressure of water at the bottom of container A.

According to the principle of inclined plane, it is labor-saving and not work-saving.

f=1000×2÷20n=100

w=mgh=1000×2j=2000j

Resistance f=

The distance traveled in 10 minutes is: s=vt=6m s 600s=3600m at a constant speed, and the resistance is equal to the traction force.

Then the work done by the motor on the bicycle is: w=fs=12n3600m=

That is, find the work done by the resistance: f = scale coefficient multiplied by mg =

s=mw=

According to g=mg, the gravity is 600n; f=0. 02g=12n；According to p=w t=fs t=fv; (v=s t)w=pt=fv*t=12n*6m s*(10*60s)=43200j("*multiplier).