P5

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• P4- Explaining motion
• Forces and interactions
• Forces always arise from an interaction between two objects
• Forces always come in pairs
• Interaction pairs are:
• Equal in size
• In opposite directions
• Two kinds of interaction:
• Contact forces
• Action- at- a distance (eg. Gravity)
• Steady speed = balanced forces
• Cars
• Engine makes the wheels turn
• Wheel rotates and exerts a force backwards on the ground
• Friction
• Between two surfaces as they slide over each other
• Friction is caused by roughness
• If object moves one force is more
• Resultant force
• Add both forces together
• Direction must be taken into account
• Vertical forces
• Always in both directions
• Still objects have a resultant force of zero
• Gets faster as the object first falls as air resistance has a greater effect
• Faster an object the more air resistance
• Describing motion
• How far they've gone is the distance
• Displacement is the shortest route
• Speed= distance/ time
• Velocity has a direction
• Acceleration is as an objects speed increases
• Acceleration= change in speed/ time for the change to occur
• A constant slope in a distant time graph shows a steady speed
• Momentum
• Momentum= Mass x Velocity
• The greater the mass the greater the velocity
• A vector quantity- size and direction
• Change in momentum depends on the porce
• Change of momentum (kg m/s)= Resultant force (N) x Time for which the force acts (s)
• Work
• Energy transferred
• Work done by a force
• Work done by a force(J)
• Kinetic energy
• Kinetic Energy (J)= 1/2 x Mass (kg) x velocity ([m/s]2)
• Kinetic energy is energy of movement
• Greater the mass the faster it is going= greater kinetic energy
• GPE
• Height energy
• GPE (J)= Weight(N) x Vertical height difference (m)
• Falling objects convert GPE into KE

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