Physics 2A Forces and their effects

Physics 2A Forces and their effects

1. acceleration and velocity time garphs

   • gradient=acceleration
   • flat sections = steady speed
   • steeper the graph
     • greater acceleration/ decleration
   • uphill (/) accelecration
     • downhill (\) deceleration
   • area under graph =distance in that time
   • curve = change acceleration
   • acceleration=
     • gradient=
       • vertical change / horizontal change

2. weight mass and gravity

   • force of attraction
     • only notice when one force is big
     • gives everything weight
     • without it acceleration would be same throughout universe.
   • mass = stuff in object
     • mass is the same anywhere in universe
       • volume
   • caused by gravity
     • weight is a force
   • weight = mass x gravitational field strength

3. resultant forces

   • overall force on object
     • most times 2 forces acting on one object
     • overall effect
       • decides the motion
         • acceleration
         • decelration
         • stop
         • constant speed
   • means change in velocity
   • object stationary
     • resultant force = 0N
       • object remain stationary
   • moving object 0N
     • keep moving at same speed/velocity
   • resultant force = more than 0N
     • object accelerate in direction of force
       • force = mass x acclecration

4. reaction forces are equal and oppostie

   • two objects interact forces exert are equal and oppostie

5. kinetic energy

   • movement energy
     • anything that moves has kinetic energy
       • kinetic energy = 1/2 x mass x speed(squared)
         • Ek = 1/2 x m x v(squared)
   • kinetic energy depends on mass and speed
     • big mass and fast speed = more energy
   • kinetic energy transferred is work done
     • kinetic energy transferred = work done by brakes
       • 1/2 x m x v (squared) = f x d

6. potential energy

   • gravitational potential energy
     • due to height
       • gravitational potential energy = mass x gravity x height
         • Ep = m x g x h
   • falling objects convert potential into kinetic
     • kinetic energy gained = potential energy lost
     • some kinetic energy is transferred into heat and sound
   • elastic objects store energy as elastic potential energy
     • any object that can return to its original shape after force is removed is elastic
       • work is done to an elastic object to change its shape
         • this energy is not lost but stored
           • elastic potential energy
             • the elastic potential energy is converted into kinetic energy when the force is removed the object returns to its original shape
     • extension of an elastic object is directly proportional to force
       • F = k x e
         • f = force applied
         • k = spring constant (depends on the material of the spring)
         • e = extentsion
       • there's a limit to the amount of force applied for the extension to increase proportionally
         • limit of proportionality
           • if you increase an object past this point it will remain permanently stretched

7. power

   • rate of doing work
     • power = work done (energy transferred) / time taken
       • P = E / t
   • power is measured in watts
     • one watt = 1 joule of energy transferred per second

8. momentum and collisions

   • momentum (kg m/s) = mass (kg) x velocity (m/s)
     • p = m x v
   • momentum is a property of moving objects
     • greater mass and greater it velocity the more momentum an object has
     • momentum before = momentum after
       • conservation of momentum
         • collision or explosion

9. car design and safety

   • forces cause change in momentum
     • large force = faster change in momentum (greater acceleration)
       • car crash
         • if someone's momentum changes quick the forces on the body will be large and cause injury
         • cars designed to safely convert kinetic energy
           • in a crash there's a big change in momentum over a short time
             • this means inside the car huge forces could be fatal
           • this is often by increasing the time over which momentum changes lessens the forces
   • crumple zones
     • front and back of the car crumple on impact
       • cars kinetic energy is converted into other forms when the car body changes shape
         • increase impact time decrease force by change in momentum
   • seat belts
     • stretch slightly
       • increasing the time
         • reducing force on the chest
   • air bags
     • gradually slow you down
       • prevent you from hitting hard surfaces in the car