P2- forces

forces between objects

• forces measured in newtons
• objects ALWAYS exert equal and opposite forces on eachother
• sometimes called action and reaction forces
• eg if you hit a barrier in your car, the barrier will exert the same size force on the car in the oppsote direction

resultant force

• resultant force is the single force which would have the same effect as all the original forces acting together
• result force is zero= if object is at rest it will stay at rest, if object is moving it will carry on moving in same direction at same speed
• when resultant force isnt zero= if object is at rest there will be an acceleration in direction of force, if object is moving in same direction as resultant force it will accelerate in that direction, if object is moving in opposite direction to resultant force= deceleration

force and acceleration

• RF always causes acceleration
• an object can accelerate by changing direction because that changes velocity
• resultant force=mass x acceleration
• greater the resultant force = bigger acceleration
• bigger the mass= the bigger the force needed to give it acceleration

on the road

• if a car is driving at steady speed= RFis zero
• the driving force on the car is equal and opposite to air resistance and friction
• faster the speed the bigger deceleration needed to stop car so…