Observing carefully the five experiments of yesterday, it should be clear that force is associated with acceleration. Whenever there is a net force acting on an object, the object will accelerate. Furthermore, experiments show that the amount of acceleration is dependent on the mass of the object. The dependence is inverse. In other words, the more massive the object the smaller will be the acceleration in a linear manner. We can use this experimental fact to define the force on an object in the following way:

Force = Mass × Acceleration or F = ma.

This property of mass is called inertia. The units of force are kilograms × meters/(second)2 which we define as being a newton. In the English system the unit of force is a pound and the unit of mass is the slug.

  1. Describe the experiment which shows that the acceleration is inversly proportional to the mass.
  2. A force gives a 2.0 kg mass an acceleration of 5.0 m/s2. What is the magnitude of the force?
  3. A 16-N force is applied to a 2-kg mass. What is the acceleration of the mass?
  4. An athlete exerts a force of 150 N on a shot put giving it an acceleration of 20 m/s2. What is the mass of the shot put?
  5. A 1.5-kg mass accelerates across a smooth table at 15 m/s2. What is the net force applied to it?
  6. What force gives a 1.0 kg mass an acceleration of 9.8 m/s2?
  7. Determine the acceleration that a force of 25 N gives to a 4.0 kg mass. The friction force to be overcome is 5.0 N.
  8. If the net force applied in the direction of motion to a certain object on a horizontal frictionless surface is doubled, the acceleration of the object is ___________?
  9. If the mass of an object increases, its inertia _______?
  10. If the sum of all the forces acting on a car is zero, the car a) must be at rest b) may be at rest c) must be moving at constant speed d) must be accelerating.