Forces

• Scalar - a quantity with magnitude only
• Vector - a quantity with magnitude and direction
• Scalar quantities:

  • Speed
  • Distance
  • Time
  • Energy
• Vector quantities:

  • Velocity
  • Displacement
  • Acceleration
  • Force
  • Momentum
• The weight of an object is directly proportional to the mass of an object
• Weight is measured in newtons.
• Mass is measured in kilograms
• The resultant force is a single force which has the same effect as all the original forces acting together.
• A single force acting at an angle can be resolved into 2 components acting at right angles to each other.
• One joule of work is done when a force of one newton caused a displacement of one metre
• 1 joule = 1 newton-metre
• Changes in shape are called deformation
• Elastic deformation - reversed when the force is removed
• Inelastic deformation - not fully reversed when the force is removed, permanent change in shape.
• Hooke's Law - the extension of an elastic object is directly proportional to the force applied.
• The limit of proportionality is when the elastic limit of a material is reached.
• A lever consists of a pivot, an effort and a load.
• Levers can act as force multipliers, allowing us to lift heavier loads than the effort force would usually allow.
• The turning effect of a force is the moment of a force.
• The pressure in fluids cause a force at right angles (normal) to a surface
• As altitude increases, the density of air decreases.
• As height increases, there are fewer air molecules above the surface
• The weight of air above the surface decreases with altitude.
• The average walking speed is 1.5 m/s
• The average running speed is 3 m/s
• The average cycling speed is 6 m/s
• The typical speed of sound in air is 330 m/s
• When an object moves in a circle at constant speed, the direction of its motion constantly changes
• When an object moves in a circular motion, velocity constantly changes. However, magnitude stays the same. Velocity
• Terminal velocity is the maximum speed attainable by an object as it falls
• Newton's First Law - an object remains at the same state of motion unless a resultant force acts on it.
• Newton's Second Law - the acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to the mass of the object
• Inertia - the tendency of an object to continue in their state of rest or of uniform motion
• Inertial mass - a measure of how difficult it is to change the velocity of an object, and the ratio of force over acceleration.
• The typical reaction time of a person is between 0.2 and 0.9 seconds
• The friction between tyres and break pads causes the kinetic energy of the vehicle to decrease, and the break pads to increase in temperature.
• How does a crumple zone decrease the force in a collision?

  • The car will crumble on impact
  • This increases the duration of the collision
  • The change in momentum remains the same
  • This decreases the rate of change in momentum
  • This decreases the force