Why Does the Car Move When Pushing a Heavier Bus?

[Dramacon]

If a car is pushing a bus (and the two both move in the direction of the car), I understand that the amount of force with which the car pushes against the bus is equal to the force the bus pushes back on the car.

What I don't understand is why the car moves. Is it going forward with the same force that it applies on the bus (and therefore receives)?

 

[PhysicsIsKing]

If I understand correctly then:
- You are correct, the car pushes on the bus with equal and opposite force
- The key point is that this is not the only force on the car. The car also pushes on the Earth and
the Earth on the car.
- This force must be bigger than the force of the bus on the car if the (bus+car) system are
to keep moving forward i.e, we have some net force in the forward direction
- Note also that the acceleration of the total (bus+car) system is now much smaller than it would for the car alone because F=ma and
1. The net force is smaller than the force the cars engine can supply
2. This smaller force must also move the mass of the bus as well as the car

Hopefully this cleared things up for you a little bit :)

 

[PeterO]

If a car is pushing a bus (and the two both move in the direction of the car), I understand that the amount of force with which the car pushes against the bus is equal to the force the bus pushes back on the car.

What I don't understand is why the car moves. Is it going forward with the same force that it applies on the bus (and therefore receives)?

You ponder whether it is going forward [a motion] with the same force that it applies to the bus [an action] ?

 

[PeterO]

If a car is pushing a bus (and the two both move in the direction of the car), I understand that the amount of force with which the car pushes against the bus is equal to the force the bus pushes back on the car.

What I don't understand is why the car moves. Is it going forward with the same force that it applies on the bus (and therefore receives)?

You mention that the car pushes forward on the bus, and the bus pushes back on the car. If that was the only forces acting, then the bus will accelerate forward and the car will accelerate back - until the forces stop.
Since the forces are contact forces, they can only continue while the car and bus are i contact.
The instant either car or bus begins to move, contact ceases and so all acceleration ceases.

BUT, both car and bus moved forward [in the direction the car was pushing on the bus.

That means there must have been at least one other force acting [actually 2 more, since all forces come in action-reaction pairs].
The car must have been pushing back on the road, so that the road pushes forward on the car. That force between car and road must be bigger than the force between car and bus, since we are told the car moves forward.

 

[Nickie]

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. In this case, the car is exerting a force on the bus, and the bus is exerting an equal and opposite force on the car. This means that the car and the bus are experiencing the same amount of force in opposite directions.

The reason the car moves forward is due to the difference in mass between the car and the bus. The car has less mass than the bus, so it accelerates faster in response to the same amount of force. This is explained by Newton's second law of motion, which states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

In simpler terms, the car moves because it is easier to accelerate a smaller mass than a larger one. So, even though the car and the bus are experiencing the same amount of force, the car has a greater acceleration and therefore moves forward.

It is also important to note that the force of the car pushing on the bus and the force of the bus pushing back on the car are acting on different objects. The force of the car on the bus causes the bus to move, while the force of the bus on the car causes the car to move. They are not directly related to each other in terms of causing motion.

I hope this explanation helps to clarify any confusion about Newton's third law in this scenario. Keep in mind that this law applies to all objects, not just cars and buses, and it is a fundamental principle in understanding the behavior of objects in motion.