forces

• what is a scalar quantity?

  • scalar quantities only have a magnitude (size)
  • e.g. speed
  • they do not have a direction
• what is a vector quantity?

  • vector quantities have a magnitude and a direction
  • e.g. velocity
• what is a contact force?

  • contact forces happen when two objects are physically touching
  • e.g. friction, tension & normal contact
• what is a non-contact force?

  • non-contact forces happen when objects are separated
  • e.g. gravitational force, electrostatic force & magnetic force
• distance-time graphs

  • y-axis : distance
  • x-axis : time
  • on a distance-time graph, movement at a constant speed is shown with a straight line
  • if an object is accelerating, we can measure its speed by drawing a tangent & measuring the gradient
• speed-time graphs

  • y-axis : speed
  • x-axis : time
  • if an object's speed is constant, the line will be horizontal
  • if the object is not moving, the line will run along the x-axis
  • if speed of object increases there will be a positive gradient
  • if speed of object decreased there will be a negative gradient
• how to work out distance travelled on speed-time graphs?

  • the area under a speed-time graph is the distance travelled
  • triangle : 1/2 x base x height
  • rectangle : base x height
• what is mass?

  • an object's mass is a measure of the amount of matter that it contains
• what is inertia?

  • an object's mass is also a measure of how difficult it is to change it's motion
  • this is called inertia
  • e.g. object with high mass has more inertia than an object with a lower mass
  • difficult to move object with high mass & once it is moving it's harder to stop
• what is the resultant force?

  • the resultant force is the sum of all of the forces acting on an object
  • the change in an object's motion is caused by resultant force
  • if forces acting on an object are unbalanced, the resultant force is acting on the object
• what is newton's first law?

  • newton's first law says that the velocity of an object will only change if a resultant force is acting on the object
  • this applies to a stationary or moving object
• what is newton's third law?

  • newton's third law says that whenever 2 objects interact, the forces they exert on each other are equal & opposite
  • if one object exerts a force on another object, then the other object must be exerting a force back