# Physics P2 Kinetic Energy

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• Kinetic Energy
• Forces and Energy
• Work done and energy transferred are measured in joules, J.
• Work is done whenever a force moves something.
• Eg. Walking up stairs, lifting objects
• Power is a measure on how quickly work is being done.
• Work done and energy transferred are measured in joules, J.
• Work is done whenever a force moves something.
• Eg. Walking up stairs, lifting objects
• P=E/t (P is the power in watts, E is work done and t is time taken.
• W=F*d ( W is work done in joules, F is th eforce in newtons and d is the distance moved in the direction of the force)
• Gravitational Potential Energy
• On earth there is always the force of gravity acting on us.
• The amount of gravitiational potential energy depends on:
• Height above ground
• Mass
• If an object is lifted work is done against gravitational force so it gains energy.
• Ep=m*g*h (Ep is the change in gravitational potential energy, mis the mass, g is gravitational field strength and h is the change in height)
• Kinetic Energy
• All moving objects have kinetic energy. The amount depends on
• Speed
• Mass
• Ek=0.5*m*v^2 (Ek is the kinetic energy in joules, m is the mass in kg and v is velocity in metres per second
• Transferring Kinetic Energy
• The pendulum is a machine that converts gravitational potential energy into kinetic energy, and vice versa.
• When the bob is at the highest point in the swing it has no kinetic energy but a maximum gravitational potential energy
• As the bob swings downward, gravitational potential energy is transferred to kinetic energy and the bob accelerates
• However some energy is transferred to heat and becomes lower at each swing
• Momentum
• A change in momentum occurswhen a force is applied to a object which can move or is moving.
• It is difficult to change the direction of a object with a lot of momentum
• P=m*v (p is the momentum in kilograms metres per second, m is mass in kilograme and v is velocity in m/s)
• Momentum depends on the direction of travel, so the momentum will change
• the object sppeds up or slows down
• the object changes direction
• Conservation of momentum means that energy can never be lost or destroyed