# How Does a Reflecting Object Gain Kinetic Energy from Radiation Pressure?

• DeepBlue
This means that their energy is lower than the incident photons, and the difference in energy is transferred to the block, giving it kinetic energy. This phenomenon is known as the Doppler effect. In summary, when radiation pressure exerts a force on an object causing it to move, the object's kinetic energy comes from the red-shifting of the reflected photons due to the movement of the object, as explained by the Doppler effect. This results in a transfer of energy from the photons to the object, causing it to gain kinetic energy.
DeepBlue
Hi,

When radiation pressure exerts a force on an object causing it to move, where does the object's kinetic energy come from, and how?

E.g. consider a perfectly reflecting solid block in vacuum. Its face is illuminated by light. From conservation of momentum, the reflection of the light from the block's surface causes the radiation force, which accelerates the block.

The block has gained KE, but it can't be absorbing the photons, since it is perfectly reflective. Does this mean that the reflected photons are actually lower energy than the incident photons? But how? Some kind of Doppler shifting going on?

Any help is much appreciated!

Exactly. The reflected photons are red-shifted by the movement of the block.

## Related to How Does a Reflecting Object Gain Kinetic Energy from Radiation Pressure?

Radiation pressure is a force exerted by electromagnetic radiation on an object. It is caused by the transfer of momentum from the photons of the radiation to the object.

## How is radiation pressure related to kinetic energy?

Radiation pressure and kinetic energy are related by the equation P = E/c, where P is the radiation pressure, E is the energy of the radiation, and c is the speed of light. This means that the greater the energy of the radiation, the greater the radiation pressure.

## What are some examples of radiation pressure?

Some examples of radiation pressure include the pressure exerted by sunlight on solar sails, the pressure exerted by lasers on small particles, and the pressure exerted by thermal radiation on objects in a vacuum.

## How does radiation pressure affect objects in space?

Radiation pressure can have a significant impact on objects in space, especially smaller objects such as comets and asteroids. It can cause these objects to change direction or speed, and can even cause them to break apart if the radiation pressure is strong enough.

## Can radiation pressure be harmful to living organisms?

In general, the radiation pressure from natural sources such as sunlight is not harmful to living organisms. However, high levels of radiation pressure from man-made sources such as nuclear explosions or medical treatments can be harmful and can cause damage to living tissue.

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