Lesson 21.1

• A net external force is needed when moving an object
• From Newton’s second law of motion, a net external force is needed for an object to accelerate
• When the force causes the box to move parallel the direction of force, work is done on the box
• Kinetic energy is present in all moving objects
• Mathematically, Newton’s second law of motion can be expressed as

  F = ma where F is for force in Newton, m is for mass in kg, and a is for acceleration in m/s2
• Mathematically, work is expressed as

  W = Fd where W is work in joules, F is force in Newton, and d is distance in meters
• If we substitute force from Newton’s second law of motion to the formula for work, then:

  W = mad
• kinetic energy is expressed as:

  KE = 1/2mv2