Forces

• Determining the resultant force

  1. When forces act in the same direction: Resultant force is the sum of the forces

  2. When forces act in opposite directions: Resultant force is the difference between the forces

  3. When opposing forces are equal: Resultant force is zero
• When forces are balanced

  The object will experience a resultant force of zero
• If an object is at rest, it will remain at rest. If an object is moving, it will continue moving at a constant speed and in the same direction
• As the apple is NOT moving, the resultant force on it must be zero. This means that the force exerted on the table (weight) is equivalent to the normal force exerted on the apple by the table
• When forces are not balanced

  The object will experience a resultant force
• How a resultant force affects state of motion


  Describes how balanced and unbalanced forces affect the motion of an object
• When forces act on an object, the resultant force on the object is zero
• Table 5.2

  • Describes how unbalanced forces affect the motion of an object
• As the apple is NOT moving, the resultant force on it must be zero
• Forces acting on an object can be in the same direction. They may also be acting from different direction(s)
• Objects with balanced forces acting on it will have no change in its state of rest or motion
• Almost without exception, there is more than one force acting on an object, the combination of all the forces acting on the object is called the resultant force
• Gravity is the force that pulls on the apple
• An apple sits on the table. Are there any forces acting on the apple?
• There are no forces acting on the apple because the desk stops any forces from acting on it
• When two or more forces act on an object, the resultant force can be found by adding up the individual forces
• The object will experience a resultant force
• The effect(s) experienced by the object will depend on this resultant force
• Objects with unbalanced forces acting on it will either speed up or slow down
• Contact Forces

  • Forces that depend on contact between two objects e.g. normal contact force, friction
• There are two forces: the desk pushes up on the apple and gravity pulls downward on the apple
• We can represent the forces acting on an object using arrows. The arrow shows the direction of the force acting in. The length of the arrow represents the magnitude (size) of the forces
• Non-Contact Forces


  • Forces that do not require direct contact between two objects e.g. gravitational force, magnetic force