forces

• walking speed

  1.5 m/s
• running speed

  3 m/s
• cycling speed

  6 m/s
• speed of sound in air

  330 m/s
• speed of light in air

  3x10^8 m/s
• car speed

  30 m/s
• train speed

  60 m/s
• plane speed

  200 m/s
• ferry speed

  15 m/s
• what is acceleration?


  change of velocity per second
• what is Hooke's Law?


  the extension of an elastic object is directly proportional to the force applied, provided the limit of proportionality is not succeeded (F = ke)
• what is mass?

  amount of matter
• what is weight?

  force of gravity
• what is an object centre of mass?


  the single point where the weight of the object is considered to act or where the mass appears to be concentrated
• what is Newton's 2nd law of motion?

  the acceleration of an object is directly proportional to the resultant force acting on the object, and inversely proportional to the mass of the object (F = ma)
• what is Newton's 1st law of motion?

  a body will continue to move at a constant velocity or remain at rest unless a resultant external force acts on it. It is sometimes known as the law of inertia
• what is inertia?


  the tendency for objects to stay moving with the same velocity
• what is Newton's 3rd law of motion

  when two objects interact with each other they exert equal and opposite forces on each other
• what is stopping distance?

  thinking distance + braking distance
• what is thinking distance?

  distance travelled during the driver's reaction time
• what is braking distance?

  distance travelled whilst under braking force
• what is momentum?


  a measure of how difficult it is to stop a moving object
• law of conservation of momentum

  in a closed system, the total momentum before an event (explosion/collision) is equal to the total momentum after the event. This is only true if there are no external forces acting on the objects that collide/explode. When only the force of the two objects colliding/exploding affects the motion of the objects the objects form a closed system.
• what is a collision?

  at least one object has momentum before the event
• what is an elastic and ineleastic collision

  elastic: objects move separately after colliding. Inelastic: objects move together after colliding
• what is an explosion?

  both objects have no momentum before the event, and the objects will move in opposite directions after the event
• how to increase drag?

  drag depends on frequency of collisions with particles in a fluid, so to increase this you need: larger surface area, denser fluid, higher speed
• general formula for a collision

  before: p1 = m1 x v1 p2 = m2 x v2 P total = p1 + p2

  during: P before = P after

  after (inelastic): P after = (m1 + m2) x v

  after (elastic): P after = (m1 x v1) + (m2 x v2)
• why aren't people killed when jumping on an airbag?

  to stop them it requires the same change in velocity, if you increase collision time you decrease acceleration since a = v-u/t

  to stop them it requires the same change in momentum, so the longer the time of the collision, the smaller the force since force = change in momentum/time taken for change
• what is a moment?

  the turning effect of a force
• the principle of moments

  for an object to be balanced, the total clockwise moment must equal the total anticlockwise moment
• how can the size of a moment be increased?

  increasing the size of the force, increasing the size of the perpendicular distance from the from the pivot to the line of action of the force
• how is a turning moment created?

  if the object is not supported beneath the centre of mass
• what is a lever used for?

  to transmit the turning effect of a force
• what is a pivot?

  the point which forces turn objects around
• what is a load?

  the force applied
• what is the effort?

  the force which moves the object
• effect of using a small radius gear wheel to turn a large radius gear wheel

  increases the turning effect on the output wheel, but reduces the speed of the output wheel
• what is a low gear?

  using a small radius gear wheel to turn a large radius gear wheel
• what is a high gear?

  using a large radius gear wheel to turn a small radius gear wheel