forces

• Force


  A push or a pull
• We cannot see a push or pull, but we can see its effects
• Force


  • Can change the speed, shape and direction of an object
  • The unit of measurement is the Newton (N)
• Newton meter or spring balance


  Can find the weight of an object or measure other pulling forces
• The Newton is named after Sir Isaac Newton
• Newton's laws


  • When the forces on an object are balanced, there is no change in the way it moves (law 1)
  • The more massive an object is, the greater the force needed to change its motion (law 2)
  • Any object will react equally and in the opposite direction to a force applied to it
• Balanced forces


  Two equal forces applied to a stationary object in opposite directions, the object does not move, change speed or direction
• Unbalanced forces


  If one force is greater than the other, the object will move in the direction of the larger force
• Resultant force

  The effect of opposing forces, can be calculated by adding or subtracting the forces
• Speed


  A measure of how fast something is moving, the amount of distance travelled over a specific time
• Mass


  The amount of matter in something, measured in kilograms
• Weight


  The downward force acting on a mass caused by gravity, measured in Newtons
• Mass has nothing to do with gravity, so it remains the same anywhere in the universe
• Weight depends on the force of gravity, and gravity depends on the size of the objects attracted to each other
• In space, there is no force of gravity since there is no celestial object to cause a gravitational force
• Because there is no gravity in outer space, objects in space are weightless
• Calculating weight


  W = mg, where "g" represents the gravitational strength
• Friction


  A force that opposes motion
• Types of friction


  • Surface friction
  • Friction in gases (air resistance)
  • Friction in water (drag)
• Friction


  • Acts opposite to the direction of motion of the object as the object rubs against another object
  • Occurs because the microscopic hills and valleys of two touching surfaces stick to each other
• Rough surfaces


  Have more microscopic hills and valleys, resulting in greater friction
• As the force pushing two surfaces together increases, the friction between the surfaces increases
• Lubricants


  Substances used to reduce friction, examples include oil, grease, and wax
• Air resistance


  The friction or drag caused when an object moves through air
• Vehicles and helmets have streamlined shapes to reduce air resistance
• A car that is travelling at constant speed has a forward thrust that overcomes friction from the tires and air resistance
• Free fall


  When the only force acting on an object is gravity, causing it to accelerate (speed up)
• Lift


  The force that acts upwards on an object, allowing it to slow down its descent
• Drag


  The force caused by friction between a moving object and the liquid or gas it is moving through
• Upthrust


  The force produced by the displaced water that pushes an object floating on water upwards
• When the total weight of an object is more than the upthrust the water can create, the object will sink