# Forces

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• Created by: Jo Wells
• Created on: 27-12-12 14:01
• Forces
• Weight, Mass & Gravity
• Weight = Mass X Gravitational Field Strength
• W = m X g
• Gravity = makes things ACCELERATE towards ground & gives everything WEIGHT
• Weight (N) = a force
• Mass (Kg) = NOT a force
• Weight = caused by pull of gravitational force
• Mass = amount of 'stuff' in an object
• Resultant Force
• = Overall force on something
• e.g. a teapot = gravity acting downwards (10N), causing a reactant force acting upwards (10N) (keeping object stationary)
• Decides MOTION of object
• Whether it will ACCELERATE, DECELERATE or stay at a STEADY SPEED
• Means a CHANGE in VELOCITY
• e.g. moving car = driving force 1000N left, with air resistance 600N right = 400N (left)
• & Acceleration
• If resultant force on a stationary object = ZERO, object will STAY stationary
• If there is NO resultant force on a moving object, it'll carry on at the SAME velocity (steady)
• If there is a NON-ZERO resultant force, object will ACCELERATE in direction of force
• starting, stopping, speeding up, slowing down & changing direction
• Resultant force (N) = mass (Kg) X acceleration (m/s squared)
• F = m X a
• Reaction forces = EQUAL & OPPOSITE
• Frictional force
• Friction slows things down
• Acts in opposite direction to movement
• DRAG from fluids (air or liquid)
• Reduce drag by STREAMLINING
• Drag increases as speed increases
• Terminal velocity
• Objects falling through fluids reach a terminal velocity
• At start, gravity = much more than frictional force, so they ACCELERATE
• As speed increases, friction increases = gradually reduces acceleration until frictional force = accelerating force
• = its maximum speed or TERMINAL VELOCITY
• Terminal velocity of falling objects depends on SHAPE & AREA