Work Done & Friction: Definition & Effect

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Work done is defined as the force multiplied by the distance moved in the direction of that force. In the context of a moving car, friction acts opposite to the direction of motion, resulting in negative work when the car is braking. Conversely, when the car accelerates, friction acts in the same direction as the motion, leading to positive work. The direction of friction is crucial as it opposes slipping between the tire and the road surface. Understanding these dynamics clarifies how friction influences the work done on a vehicle during different driving conditions.
Griff38
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If work done is defined as F X distance moved in the direction of this force, is friction doing work on a moving car since if the car is moving to the right friction is actually acting to the left? or should the definition of work done be F x distance moved parallel to the line of action of this force in which case the displacement and force can be in totally opposite directions.
 
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If the car moves to the right but friction acts to the left, then the work done will be negative. That would be the case when braking. If the car is accelerating, then the force will point in the direction of motion and the work done will be positive.
 
Thank you so much, that's made it very clear.
 
Consider a car moving forward to the right as you look at the car. This implies the the tires rotating in a clockwise direction. As a point on the tire comes around to the bottom where it contacts the road, the direction the tire is moving relative to the road is to the left. Friction, in this case, is then applied to the tire toward the right --> in the direction of the cars motion. As previously mentioned, friction acts opposite to the direction of motion. The "motion" being the motion of the tire.
 
The direction of friction depends on whether the car is accelerating or deaccelerating. Friction acts to oppose slipping between the surfaces.
 

Thread 'Mousetrap Car Energy efficiency'

For simple comparison, I think the same thought process can be followed as a block slides down a hill, - for block down hill, simple starting PE of mgh to final max KE 0.5mv^2 - comparing PE1 to max KE2 would result in finding the work friction did through the process. efficiency is just 100*KE2/PE1. If a mousetrap car travels along a flat surface, a starting PE of 0.5 k th^2 can be measured and maximum velocity of the car can also be measured. If energy efficiency is defined by...
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