Forces (physics)

• Scalar- quantity with just magnitude
• vector- quantity with magnitude and direction
• scalar- speed, distance, mass, time, temp
• vector- velocity, displacement, weight, acceleration, force, momentum, moment, inertia
• distance- length travelled between the start and end
• displacement- how far something is from the start point. involves direction, distance in a given direction
• speed- scalar, the rate of change of distance
• velocity- vector, involves direction, rate of change of displacement
• motion in a circle

  • when an object is moving in a circle at a constant speed, the velocity of the object is continually changing, because it’s changing direction
  • because the velocity is changing, the object must be accelerating
• centripetal acceleration

  • this change in direction of the velocity is towards the centre of the circle
  • the acceleration of the object that is towards the centre of the circle is called centripetal acceleration
• moment- a turning effect, a measure of a forces tendency to cause a body to rotate
• moment= force x perpendicular distance from pivot
• force multiplier- reduces the amount of force needed to move an object, increasing the speed of the object
• Principle of moment- If an object is balanced (in equilibrium ) the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot
• GEARS

  the forces acting on the teeth are identical for both gears but there moment are different

  • if a larger gear is driven by a smaller gear, the larger will rotate slowly but will have a greater moment eg. a low gear on a bike
  • if a smaller gear is driven by a larger gear, the smaller gear will rotate quickly but will have a small moment eg. a high gear on a bike
• what is momentum?

  • moving object have momentum
  • momentum is a combination of mass and velocity
  • objects have more momentum if they are: - heavier (have more mass) - moving faster
• intertia- inertia mass is a measure of how difficult it is to changle the velocity of an object

  M= F/A
• collisions

  momentum in collisions is conserved

  total momentum before a collision= total momentum after a collisions
• car safety- crumple zones

  • area of vehicle that are designed to crush in a controlled way during s collisions
  • absorbs energy from the impact and also increases the time taken to change the momentum in a crash : reduces force involved
• car safety- air bags

  • increases time taken for the heads momentum to reach 0 so reduces forced on it
  • provides soft cushion
  • large SA distributes the force of the crash
• Car safety- safety belts

  • stop you travelling forward inside the car if there is a collision
  • stretch a bit to increase the time taken for the body’s momentum to reach 0 : reduces the force on it