This discussion focuses on the application of Newton's second law to car acceleration, emphasizing the role of friction. It establishes that friction between the tires and the road not only opposes rotational motion but also facilitates translational motion, enabling the car to accelerate. The conversation highlights the importance of understanding the forces acting on both the tires and the road, particularly in scenarios where external forces appear absent, such as on slippery surfaces. Key concepts include the interaction of forces as described by Newton's third law and the dynamics of the car-Earth system.
PREREQUISITESPhysics students, automotive engineers, and anyone interested in understanding the mechanics of car acceleration and the forces involved in vehicle dynamics.
The car tyres push on the road the way our feet do when we are walking. By Newton's third law the road pushes the car in the direction of motion.abdossamad2003 said:
When a person walks, it is clear that an external force enters the sole of the foot from the ground and agrees to move in that direction, but in the case of a car, where is the direction of the reaction force and where does it enter?PeroK said:
The bottom of the tyre acts like a foot.abdossamad2003 said:
That is the force from the tire acting on the road.abdossamad2003 said:
When the car accelerates forwards, the Earth must turn imperceptibly backwards.jack action said:
This would also be just as true in the case of a rocket powered car but in that case the friction between the road and tire is not the driving force but only prevents slipping. The Earth still moves, just not as much. Momentum of the car is conserved with the Earth and the rocket exhaust.abdossamad2003 said:
It's the reaction force on the wheel from the ground.abdossamad2003 said:
No. There's no friction acting against the motion.abdossamad2003 said:
##F_t## is the force of the tyre on the road.abdossamad2003 said:
Yes, ##F_R## acts against the rotation of the wheel driven by the engine.abdossamad2003 said:
I think the reaction force shown is the friction. Friction acts between the tire and the road so there is an equal and opposite force on each. Here is a short video explanation.abdossamad2003 said:
If the car is coasting, yes. But not for the drive wheels when the car is speeding up. The tires form a contact patch with the pavement. When the car is speeding up the force of friction on the contact patch of the drive wheels is in the direction of motion.abdossamad2003 said: