Why does F=ma not apply when pushing a car with constant velocity?

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In summary, when pushing a car with a constant velocity, the net force on the car is zero according to Newton's 2nd law. This means that the force applied must be equal to the resistance or friction in order to maintain the constant velocity.
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khurram usman
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F= ma on a car...?

suppose i am pushing a toy car or a real size car with a constant velocity...say 10m/s. now as there is no change in velocity so a=0 . then according to F=ma , F=0.
but the situation seems otherwise ..that is i am applying force
 
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  • #2


khurram usman said:
suppose i am pushing a toy car or a real size car with a constant velocity...say 10m/s. now as there is no change in velocity so a=0 . then according to F=ma , F=0.
but the situation seems otherwise ..that is i am applying force
Friction with the ground is an existing force you must overcome with a counterforce in order to keep the vehicle moving at constant velocity. Once you do so, the net force on the vehicle is zero.
 
  • #3


Newton's 2nd law says that the net force must equal 'ma': ΣF = ma. If the car moves with constant velocity, there must be another force counteracting your push to give a net force of zero.
 
  • #4


The "net" force (sum of all forces) on the car is 0, so the car does not accelerate.

There is some resistance to movement of the car, perhaps due to friction; call it [itex]-F_\text{friction}[/itex]. Left to its own, the car would slow down because of this resisting force.

You are pushing the car forward with a force as well, so call this force [itex]+F_\text{pushing}[/itex].

If [itex]F_\text{pushing}-F_\text{friction} = 0[/itex], then the net force is 0 and the car continues along its merry way without a change in velocity.

Edit: Look, 2 other correct answers in the time it took me to type this!
 
  • #5


DaveC426913 said:
Friction with the ground is an existing force you must overcome with a counterforce in order to keep the vehicle moving at constant velocity. Once you do so, the net force on the vehicle is zero.

Doc Al said:
Newton's 2nd law says that the net force must equal 'ma': ΣF = ma. If the car moves with constant velocity, there must be another force counteracting your push to give a net force of zero.

so the net force should be 0 in my case
that is the force which i am applying + resistance or friction = 0?
 
  • #6


khurram usman said:
so the net force should be 0 in my case
that is the force which i am applying + resistance or friction = 0?

Yup.
 
  • #7


ok thanks
 

FAQ: Why does F=ma not apply when pushing a car with constant velocity?

What is F=ma and how does it apply to a car?

F=ma is a basic physics equation that stands for force equals mass times acceleration. In the context of a car, this equation can be used to calculate the force needed to accelerate the car based on its mass and the desired acceleration.

What are the different forces acting on a car that affect its acceleration?

There are several forces that act on a car and affect its acceleration, including friction, air resistance, and the force produced by the engine. These forces can either help or hinder the car's acceleration, depending on their direction and magnitude.

How does the mass of a car impact its acceleration?

According to F=ma, a larger mass will result in a larger force needed to produce the same acceleration. This means that a heavier car will require more force to accelerate compared to a lighter car. However, other factors such as engine power and friction can also play a role in determining a car's acceleration.

Can you explain how F=ma affects a car's braking?

When a car brakes, the force applied by the brakes results in a negative acceleration, which is known as deceleration. This deceleration is determined by the mass of the car and the force applied by the brakes, according to F=ma. The greater the force applied, the faster the car will slow down.

How does F=ma relate to the speed and velocity of a car?

By using F=ma, it is possible to calculate the acceleration of a car, which in turn can be used to determine its speed and velocity. The force required to accelerate the car, divided by its mass, will result in the acceleration. This acceleration can then be integrated to calculate the car's speed and velocity over time.

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