# P10 - Forces + momentum

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• Created by: Lucy Hart
• Created on: 19-01-20 20:14
• P10 Force + Motion
• P10.1 Force and Acceleration
• RP - investigating force + acceleration
• resultant force  = mass x acceleration
• Newton's 2nd law of motion
• greater mass of an object, the smaller acceleration (inversely proportional)
• greater the resultant force on an object, greater the object's acceleration (directly proportional)
• intertia - moving at constant velocity
• accelerates if the resultant force is the same direction as velocity
• decelerates if the resultant force is in opposite direction
• P10.2 Weight + Terminal Velocity
• weight - caused by gravitational force, newtons N
• mass - quantity of matter, kg
• weight = mass x g
• terminal velocity
• acceleration of an object decreases as it falls, frictional force increases, resultant force decreases so acceleration decreases
• terminal velocity - reaches constant velocity, frictional force on it is equal + opposite to its weight
• resultant force is zero
• P10.3 Forces + Braking
• stopping distance = thinking + braking
• thinking - distance travelled time taken for driver to react
• braking - distance travelled time the braking force acts
• factors affecting stopping distances
• tiredness, alcohol + drugs - increase reaction times
• faster a vehicle, further it travels
• wet + icy roads, have to brake with less force to avoid skidding
• worn brakes + tyres take longer to stop
• deceleration = v2 - u2        2s
• friction + air resistance oppose the driving force
• P10.4 Momentum
• momentum = kg m/s
• momentum = mass x velocity
• conservation of momentum - in a closed system, the total momentum before an event is equal to the momentum after the event
• P10.6 Impact Forces
• crumple zones - lessen force of impact
• the longer the impact time, the more the impact force is reduced
• reduced by soft pad, act as cushion, increase impact time, reduce momentum
• acceleration = change of velocity/time
• force = change of momentum/    time
• P10.7 Safety First
• cycle helmets + cushioned surfaces reduce impact forces by increasing impact time
• seat belts + air bags spread force so increase impact time
• side impact bars + crumple bars give way in an impact increasing impact time
• P10.5 Using Conservation of Momentum
• when two objects push each other apart, they move with different speeds if they are different masses but with equal + opposite momentum, so total momentum 0
• MaVa + MbVb = 0
• Untitled
• P10.8
• object is elastic if it returns to its original shape when forces are removed
• limit of proportionaliy - forces is too big, stretches more than predicted
• force = spring constant = extension
• extension of a spring is directly proportional to the force, as it doesn't exceed limit of proportionaliy