PHYS - T1 Forces

• Speed


  Distance travelled per unit time
• Acceleration


  Change in velocity per unit time
• Velocity

  Speed in a given direction

  
• Units


  • Distance in metres (m), Time in seconds (s), Speed and Velocity in metres per second (m/s), Acceleration in metres per second squared (m/s^2)

  
• Distance-time graph


  Gradient is velocity, Negative gradient is returning to starting point, Horizontal line is stationary, Distance zero is back at starting point, Curved line is accelerating

  
• Velocity-time graph


  Gradient is acceleration, Negative gradient is deceleration, Speed zero is at rest, Horizontal line is constant speed, Area under line is distance travelled, Curved line is changing acceleration

  
• Vector


  Has magnitude and direction
• Scalar


  Has just a magnitude
• Examples of Scalars


  • Distance, Speed, Time, Energy

  
• Examples of Vectors


  • Displacement, Velocity, Acceleration, Force
• Forces


  • Can change speed, shape or direction of a body, Measured in Newtons (N)

  
• Friction


  Force between two surfaces which impedes motion and results in heating, Air resistance is a form of friction
• Finding resultant of forces


  Add if in same direction, Subtract if in opposite direction
• Newton's first law


  An object has a constant velocity unless acted on by a resultant force
• Newton's third law


  Every action force has an equal and opposite reaction force
• Mass

  Measure of how much matter is in an object, Measured in kilograms (kg)
• Weight

  Gravitational force, Effect of a gravitational field on a mass, Calculated as Mass x Gravitational field strength
• Gravitational field strength on Earth is 10N/kg
• Weight of an object acts through its centre of gravity
• Motion of a body falling in a uniform gravitational field


  Initially no air resistance, only weight force, Acceleration increases speed and air resistance, Resultant force decreases, Acceleration decreases, Terminal velocity reached when forces balance
• Thinking distance


  Distance travelled between driver realising need to brake and pressing brakes, Increased by greater speed, slower reaction time
• Braking distance


  Distance travelled between pressing brakes and vehicle stopping, Increased by greater speed, mass, poor road/car conditions
• Stopping distance


  Sum of thinking distance and braking distance
• Deformation


  Change in size and shape of a body due to a force
• Elastic deformation


  Object returns to original shape when load removed, Example: Stretching a spring
• Force-extension graph


  Linear graph follows Hooke's law, Curved graph does not follow Hooke's law, Limit of proportionality where it stops being linear
• Acceleration = 


  Change in velocity / total time
• (final speed)^2 =


  (initial speed)^2 + (2 x acceleration x distance)