1 PHYSICS

• Force can be operationally defined based on observed effects
• Forces do not always cause motion
• Forces


  Can produce changes in motion
• Changes in motion


  • A boy pushing a wall
  • A woman throwing a ball
  • A girl sitting on a chair
• In Grade 7, you learned displacement, velocity, and acceleration
• Activities helped understand and make visual representations of the motion of objects such as motion graphs
• Uniform motion


  Objects moving in straight line at constant speed
• Non-uniform motion


  Object covers unequal displacements at equal intervals of time
• When a car starts moving


  It speeds up
• When a car nears a stop sign

  It slows down
• Most of the motions we come across in our daily life are caused primarily by force
• A ball will not move when there is no force applied to it
• If you push the ball, it will move or roll across the surface of the table
• When you push the ball in the direction of its motion, it moves faster and farther
• When you push the ball opposite to the direction of its motion, it may slow down and eventually stop
• When you push the ball in a direction different from its original direction of motion, it changes direction
• Magnitude


  Refers to the size or strength of the force
• Direction


  Points to where the object goes
• Point of application


  The location of where the force is applied
• Line of action


  The straight line passing through the point of application and is parallel to the direction of force
• Types of force


  • Contact forces
  • Non-contact forces
• Contact forces


  • Forces where objects touch or contact with each other
• Contact forces


  • Applied
  • Friction
  • Normal
  • Tension
• Applied force


  A force given to a person or object by another person or object
• Friction


  The force acting against or opposite an object in contact
• Normal force


  The force that acts perpendicular to the surface of the object in contact
• Tension


  The force applied to string, rope, chain or cable
• Non-contact forces


  • Forces where objects do not touch or contact with each other
• Non-contact forces


  • Gravitational
  • Magnetic
• Gravitational force


  The force of attraction between two objects
• The weight of an object is an example of the gravitational force of the Earth towards the object
• The weight of an object depends on the mass of the celestial body where the object is attracted to
• Balanced forces


  Forces that are equal in magnitude but opposite in direction
• Balanced forces do not cause a change in motion
• Unbalanced forces


  Forces that cause a change in the motion of an object
• Net force or resultant force is the sum of all forces acting on an object
• When an object is at rest, a zero net force would make the object remain at rest
• When the net force is not zero, the object’s velocity will change
• Forces can be applied to objects in different directions at the same time
• It is important to identify all the forces acting on the object which cause change in the motion