# Physics P2 Forces and their effects

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• Forces and their effects
• Resultant Forces
• A stationary object remains stationary if the sum of the forces acting on it is zero.
• If an object has multiple forces acting on it-then the resultant force is ALL forces added together.
• When forces are balanced then the resultant force is zero and would mean that...
• A stationary object remains stationary
• A moving object keeps on moving at the same speed and in the same direction
• Non-zero resultant forces
• When the forces are balanced the resultant force is not zero
• This means that a stationary object accelerates in the direction of the resultant force
• Effects of a non-resultant force
• The object was already moving so moves faster than before
• The object is still but begins to move upwards
• The bar was de-celerating so de-celerates faster.
• Force,Mass and acceleration
• An object will accelerate in the direction of the resultant force. A force on a large mass will accelerate the object less. doubling mass halves mass
• Acceleration= force/ mass
• Forces and Motion
• Distance time graphs
• When going across the objectis stationary
• Speed= distance/time
• Velocity time graph
• Velocity is speed in a particular direction
• Different velocities (eg 2 cars)
• Different speed in the same direction
• Same speed but different directions
• Different speeds in different directions
• Across the graph is constant velocity
• Acceleration
• a=(v-u)/t  (a= acceleration, v+ the final velocity, u=starting velocity and t is time)
• Forces and Braking
• The stopping distance on a car depends on 2 things- thinking distance and braking distance.
• When a vehicle is travelling at a steady speed the engines force is balanced by air resistance.
• Potential forces
• The driving force- from the engine
• Reaction force on wheels- moves the car up
• Friction- between roads and tyres
• Gravity- downward force
• Air resistance- slows down the object
• For something to slow down two things have to occur
• The resistive forces must be increased
• The driving force must be reduced
• Stopping distance= thinking distance + braking distance
• Thinking distance is the distance for a driver to brake.
• This could be increased by tiredness, distractions, alcohol , drugs
• Braking distance is the time taken to stop
• This could be increased by poor brakes, weather conditions
• Forces and terminal velocity
• Falling objects have two main forces acting on them: the weight and air resistance
• The 3 stages of falling. At the start, the object accelerates downwards due to weight
• Then air resistance increases
• Then the objects weight is equalled by air resistance- its terminal velocity
• Weight is the force acting on an onject- a result on gravity
• W=m*g
• Forces and elasticity
• A force acting on an object can change the shape of an object
• Hookes law- the length of a spring is directly proportional to the force applied
• F=k*e (f is force, k is a spring constant and e is extension
• However, all elastic objects have a different elastic limit