Strong and handsome talk about physics

Q: What's the matter with "birds swimming in the water and fish flying in the sky"?

This belongs to Jiuzhaigou.

Magical phenomenon

Explain it first? (Knowledge of physics)

Guan Jian said: How can I see fish flying in the sky?

A: Birds swim in the water: it is the reflection of birds in the water.

virtual image

Fish flying in the sky: it is the virtual image of the reflection of the sky in the water. What people see is that the virtual image refracted by fish is mixed with the virtual image of the sky in the water.

be together

Later generations think that "fish fly in the sky"

In the proposed experimental device, as shown in the figure, both ends of the box are equipped with

spring

Put a piece of wood in the middle and put the wood in the

towards the left

In the process of pushing (

)

A, the potential energy of the left spring increases and the potential energy of the right spring decreases.

B, the potential energy of the right spring increases and the potential energy of the left spring decreases.

C, the potential energy of springs at both ends increases.

D, when the block is at the midpoint, the potential energy of the springs at both ends is the smallest.

There are two answers, C and D.

C: Under the action of force F, the box moves to the left, and the wood blocks in the box are affected.

inertia

The role of production

Go right.

Force F 1, F=FI, (energy conservation). If the box is to be removed now, under the action of F 1, the block moves to the right relative to the box, but there are springs on both sides of the block, so F 1 will convert the potential energy of the spring. The difference is that the spring on the left is in tension and the spring on the right is in compression.

Elastic potential energy

Both have increased.

d； This answer holds no matter what the box is doing, as long as the wood block is at the midpoint, the potential energy of the two springs is absolutely minimum.

Doudou ran and played on the ground with a force of 300N, pulling a 5kg iron block, and ran for 200m all the time. As soon as he turned around, it was too hot. Do you know how much the temperature has risen? What if you lose 60%?

This problem is considered from the perspective of energy, not from the perspective of force.

1. Start and

Last minute

Iron blocks are stationary, and the kinetic energy of the whole process becomes zero;

Assuming that the ground is flat, then

Gravitational potential energy

The change is also 0; The elastic potential energy has not changed; To sum up, the change of mechanical energy is 0.

Therefore, all the work done by 300N force should be converted into heat energy: 300 n.

x

200 meters

=60000J

ferreous

specific heat

0.46×10e3j/(kg℃).

The mass is 5 kilograms,

So the increased temperature is 60000/(5

x

460)

=26.087℃

2. If you lose 60%, it means you lose 60% of the heat energy, leaving 40%.

x

60000J

=

24,000 joules

The elevated temperature is

24000/

(5

x

460)

=

10.435℃

why

Stars in the sky

Twinkle, twinkle?

Careful observation, only

star

Just a flash,

planet

It doesn't flash. Why? The secret can be found under the telescope: the stars are too far away-

The nearest star

distance

earth

It's 4.6 light years-

to the end

Look, this is just a

main points

And this planet is very close and looks like a round surface on the earth. What does this have to do with flashing or not? Because we stick it out.

atmosphere

Observing the stars, there are impurities and disturbances in the atmosphere, and a little light of the stars is easily disturbed to form flicker, while the planet is a small round surface (although it is also a point to the naked eye) and consists of countless points.

light-spot

Constitute. So the anti-interference ability is much stronger, and it doesn't seem to flash. Let's get this straight!

The density of air (medium) is different, that is, near.

ground temperature

The temperature difference with the sky is large, and the stars are scattered.

The light of

Or whether the reflected light passes through.

Uniform dielectric

Sometimes when the transmission line is off, the air keeps flowing, so it seems that the light from the stars is flashing.