P5 Spaced Learning Forces

Forces can be either…………….. Contact Non-contact Friction Air resistance Upthrust Gravity Magnetism Electrostatic Forces can make things……..speed up, slow down, change direction, change shape Quantities can be either………. Scalar quantities……..only have a magnitude (size) Vector quantities……..have a magnitude and direction Temperature Energy Mass Speed Distance Force Acceleration Velocity Displacement Vector quantities can be represented with an arrow to show the magnitude and direction

Resultant force…… …..the overall force acting on a body Add together forces in the same direction, subtract forces in the opposite direction If an object has a resultant force acting on it, it will change velocity If an object has no resultant force acting on it, it will stay at the same velocity, which might be 0 if it was stationary to start with The larger the resultant force, the more the object will accelerate, but the larger its mass, the less it will accelerate, unless you increase the size of the resultant force

Key Equations Force = mass x acceleration What force is needed to make a mass of 25kg accelerate at 2.5m/s2? F = m x a = 25x2.5 = 62.5N Weight = mass x gravitational field strength What is the weight of a 70kg man on Earth, where gravitational field strength, g=10N/kg? W = m x g = 70 x 10 = 700N Work = Force x distance How much work will a woman do if she uses a force of 250N to push a box 5m? W = F x s = 250 x 5 = 1250J Force = spring constant x extension What force is needed to extend a spring by 0.15m (15cm) if its spring constant is 30N/m? F = k x e = 30 x 0.15 = 4.5J Ee= 0.5 x spring constant x extension2 How much energy is stored in a spring if it has a spring constant of 40N/m and an extenson of 0.2m? Ee= 0.5 x k x e2= 0.5 x 40 x 0.2 x 0.2 = 0.8J Moment = Force x distance from pivot What moment is produced by boy turning a spanner, when he applies the force of 60N at a distance of 0.2m from the pivot? M = F x s = 60 x 0.2 = 12 Nm

Key Equations Distance moved = speed x time How far will a car move in 60s if it is moving at 17m/s? S = v x t = 17 x 60 = 1,020m Acceleration = change in velocity ÷ time taken What is the acceleration of a car if it accelerates from 15m/s to 20m/s in 10s? a = (v – u)/t = (20-15)/10 = 5/10 = 0.5m/s2 Force = mass x acceleration What force is required to make a 60kg cyclist accelerate at 1.5m/s2? F = m x a = 60 x 1.5 = 90N Pressure = Force / Area What pressure is produced by a force of 70N spread across an area of 0.5m2? P = F/A = 70/0.5 = 140N/m2

The larger the force applied to a spring, the more its extension The larger the force applied to a spring, the more its extension. The force is proportional to the extension, up to the elastic limit, where the spring becomes permanently deformed. A moment is the turning effect of a force. The larger the distance between the force and the pivot, the larger the moment. Also, the larger the force, the larger the moment

The stopping distance of a car is made up of a thinking distance and a braking distance added together. The thinking distance is the distance travelled in the driver’s reaction time, before the brake is applied. The braking distance is the distance travelled once the brake is applied, until the car stops Increases thinking distance Increases braking distance Tiredness Drinking alcohol Taking drugs Being distracted Rainy or icy roads Worn brakes Worn tyres