Forces and Motion

• Average speed = total distance/total time
• In a distance time graph , when the line is horizontal that means the object isn't moving.
• The slope , or gradient, of a distance-time graph tells you the speed.
• A curved slope in a distance/time graph represents speed.

  A straight upward slope/line represents steady speed.
• When the speed of something changes we call that acceleration.
• A straight line gradient in a speed/time graph shows constant acceleration.
• Acceleration: when the speed of something increases.
• A horizontal line in a speed/time graph shows constant speed.
• Terminal velocity: the maximum velocity (speed) attainable by an object
• Formula for acceleration:

  Change in speed/time = final speed-starting speed/time
• Unit for acceleration: m/s squared
• If the final speed is lower than the starting speed, it means that the object is slowing down or decelerating. The acceleration is negative.
• The distance-time graph shows how the distance moved changes with time
• In a distance time graph, If the line is steeper the object is moving faster.
• In a distance time graph if the line is curved, the speed is changing
• The gradient of a line on a speed/time graph tells you about its acceleration.
• Resultant force: the total amount of force acting on an object or body along with the direction of the body.
• Balanced forces: If the forces on the object are the same size and cancel out but in opposite directions.

  Unbalanced forces: if the forces are not equal and on opposite sides.
• If you know the size of each force acting on an object, you can work out the resultant force.
• If there is not resultant force, that means the forces cancel each other out and are balanced forces.
• What happens to an extension of a spring when more mass is added to it?

  The extension of the spring is increases till the elastic limit.
• Elastic limit: the maximum flexibility the spring is able to achieve.
• Moment: the turning effect of a force
• A moment is measured in newton metres (Nm)
• Moment (Nm) = force (N) x perpendicular distance from the pivot (m)
• equilibrium: a state in which opposing forces are balanced.
• The principle of moments: When a body is balanced, the total clockwise moment about a point equals the total anticlockwise moment about the same point.
• To know if an object is balanced you need to calculate the anticlockwise moment and clockwise moment.
• Force is measured in newtons (N).

  Area is measured in metres squared (m2)

  Pressure is measured in newtons per metre squared (N/m2)

  1 N/m2 is also called 1 Pascal
• Pressure = force/area

  Force = pressure x area

  Area = force/pressure
• A force of 20N is spread over an area of 4cm squared.

  What is the pressure?

  Pressure= force/area

  = 20N/4cm2

  = 5N/cm2