Motion

• Distance is a scalar
• Displacement is a straight line from start to finish (vector)
• Equation for speed: speed = distance/time
• Definition of velocity: speed with direction
• Distance-time graph gradient shows speed
• Equation for change in velocity with unit: acceleration(m/s2) * time taken = change in velocity(m/s)
• Equation of velocity: distance/time
• Another equation for velocity: (final velocity)2 - (initial velocity)2 = 2 * acceleration * distance
• Acceleration when object falls freely is 9.8 m/s2
• Terminal velocity is the maximum speed of an object, reached when the forces moving the object are balanced by its frictional forces
• Objects in fluid experience resultant forces and acceleration decreases until resultant force is zero and object is at constant velocity
• Newton's first law states that if the resultant force is zero, then the object is stationary or moving at the same speed along a straight line
• Constant speed means resistive force = driving force
• Inertia is an object's tendency to remain at rest or moving at a constant speed. Inertia mass (kg) = force(N)/acceleration(m/s2)
• Inertia Mass is a measure of how hard it is to change an object's velocity
• Newton's second law states that acceleration of an object is proportional to the resultant force acting and inversely proportional to the mass of the object. Equation for resultant force: mass * acceleration
• Newton's third law states that when two objects interact, the forces exerted are equal and opposite
• Factors that affect braking distance and reasons:

  • Speed: high speed increases braking distance
  • Force: high braking force reduces braking distance
  • Mass: high mass of load increases braking distance
  • Weather: icy/wet roads mean less friction, increasing braking distance
  • Vehicle maintenance: worn brakes or tires increase braking distance
  • Road condition: poor road surfaces can increase braking distance
• Reactions can be slower due to drinking, taking drugs, being tired, or distracted
• Braking distance is directly proportional to velocity squared and mass, and indirectly proportional to braking force. Equation for braking distance: Braking distance = 0.5 * mass(kg) * velocity2 (m/s))/braking force
• Brakes get hot at high speeds, making them less effective
• Thinking distance is directly proportional to speed and the minimum distance between cars
• Equation for momentum: momentum = mass * velocity
• Equation for change of momentum: Force = change of momentum/time
• Closed system means no external forces act on the system
• Changes in momentum occur in a short time because large forces act
• Required practical for Acceleration:

  Aim: Investigate the effect of varying the force on the acceleration of an object of constant mass

  Variables: Independent = force, dependent = acceleration, control = mass

  Equipment: Metre ruler, toy car, weight stack, bench pulley, string, two stands, clamps, bosses, Blu-Tac or rubber bands, chalk, stopwatch

  Method: Draw straight lines perpendicular to the edge of the bench, attach the car to the string, attach the weight stand, release the weight stand and time the car hitting the pulley
• Required practical for Extension:

  Secure a clamp stand to the bench, attach bosses to the clamp stand, attach the spring and ruler to the clamps, adjust the ruler to be vertical, measure and record the unloaded length of the spring, hang a 100 g slotted mass carrier from the spring, add more masses and record the new lengths of the spring
• Centre of mass is the point through which the weight of an object can be considered to act
• Crumple zones are designed to lessen the force of impact
• Equation for force: (mass (kg) x change of velocity (m/s)) divided by time taken (s)
• Impact force decreases when you increase impact time
• When two vehicles collide, impact force is exerted equal and opposite on each other at the same time. Total momentum is conserved
• Helmets are designed to increase impact time and reduce force of impact
• Without a seatbelt, a passenger would hit the windscreen and suffer major injury
• Seat belts stop the wearer from moving forward when the car stops
• Seatbelts reduce force from decelerating by spreading out the force and airbags help by spreading the force of impact across the upper body, increasing impact time and lowering the effect of force
• Child car seats reduce deaths and serious injuries of children in cars
• Equation of stopping distance: braking distance + thinking distance
• Thinking distance is proportional to speed and braking distance is proportional to speed squared