# Momentum

Momentum is a measure of how much mass an object has and how fast it is moving. It is calculated by multiplying the mass of the object by its velocity.

• Momentum is a vector quantity, which means that it has both magnitude and direction.
• Momentum = mass x velocity.
• Momentum is conserved, which means that the total momentum of a system remains constant unless an external force acts on the system.
• Momentum can only be transferred between objects, not created or destroyed.
• Examples of momentum:
• A bowling ball has more momentum than a baseball because it has more mass.
• A car moving at 60 mph has more momentum than a car moving at 30 mph.
• A rocket launching into space has a lot of momentum because it has a lot of mass and it is moving very fast.
##### Momentum & photons
• Photons are massless particles, but they can still exert a force on other objects. This is because photons have momentum and can interact with matter through the electromagnetic force:
• Photons have no rest mass, but they do have momentum.
• Photons can interact with matter through their momentum.
• Photons can also interact with matter through the electromagnetic force.
• The interaction of photons with matter can be used to explain a variety of phenomena, such as reflection, refraction, and absorption.
• The fact that photons have momentum and can interact with matter through the electromagnetic force means that they can exert a force on other objects.
• Here are some other examples of how photons can exert a force on other objects:
• Radiation pressure: Radiation pressure is the pressure exerted by photons on a surface. It is responsible for the tails of comets, which point away from the sun.
• Light pressure: Light pressure is the force exerted by photons on a particle. It is used in optical tweezers to trap and manipulate small particles.
• Photoelectric effect: The photoelectric effect is the emission of electrons from a metal surface when it is illuminated by light. It is caused by the transfer of momentum from the photons to the electrons.
• 1
• 2

Summary