forces

• Scalar quantities


  Have only size (magnitude) and no direction
• Vector quantities


  Have both size and direction
• Speed

  Rate of change of distance
• Speed formula


  v = s/t
• v


  Speed (m/s)
• s


  Distance (m)
• t


  Time (s)
• Distance


  Total distance travelled in any direction and time
• Distance-time graphs


  • Shows when an object is stationary or travelling at a constant speed or accelerating
• Types of motion

  • Stationary
  • Steady
  • Shifted
  • Accelerating
  • Decelerating
• Displacement


  Distance from starting point in one direction
• Displacement-time graphs


  • Shows how the displacement of a moving object changes with time
• total momentum before an event = total momentum after the event
• What happens to weight and air resistance when a falling parachuter opens their parachute?


  Weight: stays the same Air resistance: increases
• Shows elastic potential energy

  
• Newtons 3rd law

  Whenever two objects interact, they exert equal and opposite forces on each other.
• A force is a push or pull that acts upon an object as a result of that object's interactions with its surroundings.
• An object's spring constant is a measure of how many Newtons of force it would require to stretch (or compress) the object by 1 metre. It has the units N/m.
• A higher spring constant means the spring is more firm (harder to stretch). A lower spring constant means the spring is less firm (easier to stretch).
• The resultant force is the overall force acting on an object, taking into account all the different forces acting on it.
• When there is a car crash, the car and the passengers decelerate rapidly.

  They experience large forces because of the very fast change in momentum - and these large forces can cause injuries.
• Speed is a scalar quantity as it only has a magnitude.

  Velocity is a vector quantity as it has both a magnitude and a direction.

  Both measure how fast you're going, but only velocity tells you the direction you're going in.
• Acceleration is a vector quantity because it tells us not just how much we are speeding up, but also which way we are turning.
• Inertia is the tendency of objects to keep moving at their current speed and direction unless acted upon by another force.
• Newton’s first law states that if no net resultant force that acts on an object then the object will continue to move at a constant velocity forever.
• Newton’s first law states that if no unbalanced forces act on an object then its velocity will remain constant. This is known as inertia.
• A force acting through a distance causes work done. The unit of work done is joules (J)
• Equilibrium: all forces acting on an object balance out
• Contact forces:

  Weight

  Electromagnetism

  Magnetism
• A contact force is any force that occurs as a result of two objects making physical contact with each other.
• By crumpling over time they increase the time taken for the passengers momentum to reach zero, and so reduce the forcesacting on the bodies of the people in the car. 
• The force of air resistance is caused by a moving object colliding with air particles
• The resultant force of an object falling at terminal velocity is zero.
• Why do falling objects reach terminal velocity?


  1. As an object accelerates and its velocity increases, the force of the air resistance will also increase.
  2. At some point, the force of weight acting downwards will equal the air resistance upwards, so there will be no resultant force.
  3. This means that there will no longer be any acceleration and the velocity of the object will stay constant.
• Terminal velocity is the maximum velocity attainable by an object as it falls through a fluid (either a liquid or gas). 
• Distance is a scalar quantity as it only has a magnitude.

  Displacement is a vector quantity as it has both a magnitude and a direction.

  Displacement is the shortest distance between the start and end points. 
• Small gears will rotate more quickly.
• Inelastic deformation is a change in the shape of an object, which cannot be reversed once the forces causing it have been removed.

  So the object will not return to its original shape. 
• Seat belts stop you flying out of your seat during a car crash.

  By stretching a little bit, they increase the time taken for the body's momentum to reach zero, and so reduce the forces on acting on the body.
• Elastic Limit: The point at which an object being stretched stops deforming elastically, and starts deforming inelastically.