Physics

# Section Summary

PhysicsSection Summary

## 9.1Work, Power, and the Work–Energy Theorem

• Doing work on a system or object changes its energy.
• The work–energy theorem states that an amount of work that changes the velocity of an object is equal to the change in kinetic energy of that object.The work–energy theorem states that an amount of work that changes the velocity of an object is equal to the change in kinetic energy of that object.
• Power is the rate at which work is done.

## 9.2Mechanical Energy and Conservation of Energy

• Mechanical energy may be either kinetic (energy of motion) or potential (stored energy).
• Doing work on an object or system changes its energy.
• Total energy in a closed, isolated system is constant.

## 9.3Simple Machines

• The six types of simple machines make work easier by changing the fd term so that force is reduced at the expense of increased distance.
• The ratio of output force to input force is a machine’s mechanical advantage.
• Combinations of two or more simple machines are called complex machines.
• The ratio of output work to input work is a machine’s efficiency.