Power and Forces: Exploring the Relationship

In summary: So in this case, the power due to friction is actually helping the car by reducing the work it needs to do to maintain its speed.
  • #1
eroxore
23
0
Hello forum.

I am finding it hard to wrap my mind around the concept of power when considering forces. We can derive [itex]\text{P} = \text{F} \cdot v[/itex] but what now does the symbol F really signify?

Is it (1) the net force on an object or (2) can we simply put in any force for F acting on an object? If the net force were to be zero in case (1), then P would be zero but that does not make any sense since driving a car with constant velocity surely requires provision of energy (right?).
In (2), what can we say about a frictional force acting on the object? Does it have som power which can attributed to it?

I would really appreciate if you could help me fathom the relationship between power and forces!
 
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  • #2
eroxore said:
. We can derive [itex]\text{P} = \text{F} \cdot t[/itex] but what now does the symbol F really signify?
Power is F*D/t.
If the net force were to be zero in case (1), then P would be zero but that does not make any sense since driving a car with constant velocity surely requires provision of energy (right?).
Right, so you can calculate power for any force acting in the direction of motion or against it. You could say that the car has a net power of zero acting on it or that it has a power from the engine of X and and a power due to friction of -X.
 
  • #3
russ_watters said:
Power is F*D/t.

You are right, sorry about that; all fixed now!

russ_watters said:
Right, so you can calculate power for any force acting in the direction of motion or against it. You could say that the car has a net power of zero acting on it or that it has a power from the engine of X and and a power due to friction of -X.

Ok, I then understand that it is not the net force on the object. I understand that it can have power from the engine but the power from air cannot be a property of the car right? The air does work on the car, so it is the rate of the air which is the friction-power, right?

One more thing: If the net force is zero, then you are not changing the speed (energy) of the object and thus it moves in a constant speed. How does power come into play in that case? Moreover, what can be said about power due to the frictional force from the wheels of the car?
 
  • #4
eroxore said:
Ok, I then understand that it is not the net force on the object. I understand that it can have power from the engine but the power from air cannot be a property of the car right? The air does work on the car, so it is the rate of the air which is the friction-power, right?

Personally I'd say it's the car doing work on the air, but that's just how I look at it.

One more thing: If the net force is zero, then you are not changing the speed (energy) of the object and thus it moves in a constant speed. How does power come into play in that case? Moreover, what can be said about power due to the frictional force from the wheels of the car?

You're not changing the speed of the car, but you ARE changing the speed of the air. That's why when you get behind a semi truck you can save a lot of gas. The truck has a small pocket of air behind it that's traveling in the same direction, so you don't do nearly as much work on the air, reducing the amount of fuel it takes to maintain your speed.
 
  • #5


Dear forum member,

Thank you for bringing up this interesting topic. The relationship between power and forces is indeed a complex one. To answer your question, let's first define what we mean by power and force.

Power is the rate at which work is done or energy is transferred. It is a measure of how quickly a force can do work. In other words, power is the amount of energy used per unit time. On the other hand, force is a push or pull that can cause an object to accelerate or change its motion.

Now, going back to your question, the symbol F in the equation P = F * v represents the net force acting on an object. This means that it takes into account all the forces acting on the object, both in magnitude and direction. In the case of a car moving at a constant velocity, the net force may be zero because the forces acting on the car (such as the engine force and air resistance) are balanced and cancel each other out. However, this does not mean that there is no power being used. The engine is still producing power to maintain the car's velocity, but the net force may be zero because the car is not accelerating.

In the case of a frictional force, it does contribute to the overall power being used. Friction converts some of the energy into heat, which is a form of energy transfer. However, the amount of power produced by friction may be small compared to other forces such as the engine force.

In summary, power and forces are closely related, but they are not the same thing. Power is a measure of how quickly a force can do work, while force is a push or pull that can cause an object to accelerate. The net force takes into account all the forces acting on an object, and even if it is zero, power may still be used to maintain a constant velocity. I hope this helps to clarify the relationship between power and forces. Keep exploring and asking questions!
 

1. What is the difference between power and force?

Power and force are often used interchangeably, but they refer to different concepts. Force is a physical quantity that describes the interaction between two objects and is measured in units of Newtons (N). Power, on the other hand, is a measure of how quickly work is done, and it is measured in units of Watts (W).

2. How are power and force related?

Power and force are related through the equation P = F * v, where P is power, F is force, and v is velocity. This equation shows that power is directly proportional to force, meaning that an increase in force will result in an increase in power.

3. What is the role of power and force in everyday life?

Power and force play a crucial role in our daily lives. Force is responsible for movement and the interaction between objects, while power is necessary for doing work. From lifting objects to driving a car, both power and force are constantly at play in our daily activities.

4. How do we measure power and force?

Power is measured using a device called a dynamometer, which can measure the amount of force applied to an object and the distance it moves. Force can also be measured using a spring scale or a force gauge, both of which measure the amount of force applied to them.

5. What are some real-life examples of the relationship between power and force?

One example of the relationship between power and force is a car engine. The more force the engine produces, the faster the car can move, and the greater its power. Another example is a person using a lever to lift a heavy object. By applying a small amount of force over a longer distance, they can produce a greater amount of power to lift the object.

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