Question Regarding Force Being Equal, Even Moving Upwards (if V=0)?

  • #1
Ascendant0
152
33
I understand based on the equation F = ma that if there is no acceleration, the forces on the object all balance out to 0 in all directions.

What I don't get is for example, slowly lowering a heavy stone slab at a constant velocity v, and raising it way above my head as high as I can at a constant velocity v, would be considered to be the same force (since my force on it would be equal to the normal force since there's no acceleration). Obviously, it's going to be a LOT harder raising that stone slab overhead as it would be slowly lowering it. It would take a lot more effort, yet according to the force equation, I'm still applying the same force. That to me is a bit confusing.

I'm thinking I'm just viewing "force" conceptually wrong here, but if someone could help me make more sense of why this is the case in the above example, I'd greatly appreciate it.
 
Physics news on Phys.org
  • #2
Ascendant0 said:
It would take a lot more effort
Your perceived effort is a very poor measurement of force. It is exceptionally difficult for humans to do constant velocity motions or to accurately gauge the force applied during different movements. The perceived effort will also involve the motion of your own body, not just the external object.

You should always avoid human-perception based explanations. Replace a human with a spring or something similarly easy to analyze. A spring will elongate by the same amount if you are raising or lowering a mass at constant velocity.

In short, the physics definition is correct, but humans are complicated.
 
Last edited:
  • Like
Likes Ascendant0 and russ_watters
  • #3
Ascendant0 said:
I'm thinking I'm just viewing "force" conceptually wrong here,
Correct. At the very least, you have to consider the work done, which is positive when raising something, and negative when lowering something at constant speed.

However, for physiological reasons, doing negative work with your muscles doesn't recharge your body (like regenerative braking would). You still consume energy, and it might even be more exhausting to your muscles to operate like this.
 
Last edited:

FAQ: Question Regarding Force Being Equal, Even Moving Upwards (if V=0)?

1. What does it mean for force to be equal when moving upwards with a velocity of zero?

When an object moves upwards with a velocity of zero, it means that the object is momentarily at rest at that point in its ascent. The forces acting on it, such as gravity and any applied force (like tension or lift), are balanced. This condition results in a net force of zero, which is why the object is not accelerating despite being in an upward motion.

2. How can an object move upwards if the velocity is zero?

An object can move upwards with a velocity of zero when it reaches the peak of its trajectory. At this point, the upward force (if any) is equal to the downward gravitational force, resulting in zero net force and, consequently, zero acceleration. The object is in a state of equilibrium momentarily before it starts to descend.

3. What forces are involved when an object is moving upwards with V=0?

The primary forces involved include gravitational force acting downwards and any applied force acting upwards, such as tension in a rope or lift from a propeller. When these forces are equal in magnitude, the object can remain stationary at that height, resulting in a velocity of zero.

4. Does the concept of force being equal apply to all objects moving upwards with V=0?

Yes, the concept applies universally to any object moving upwards with a velocity of zero, regardless of its mass or the forces acting upon it. As long as the net force is zero, the object can remain at rest at a certain height, regardless of the specific forces involved.

5. What happens to the forces if the object starts moving upwards again?

If the object starts moving upwards again, it means that the applied force has exceeded the gravitational force acting on it. This results in a net upward force, causing the object to accelerate upwards. The balance of forces shifts, and the object will have a positive velocity as it continues to ascend.

Similar threads

I Origin of Centripetal force when the net force toward the center is 0?
Replies
8
Views
2K
I Acceleration as a Function of Time Using Constant Power
Replies
27
Views
2K
I Fluid dynamics: drag coefficient and pressure at the stagnation point.
Replies
1
Views
968
B Maximum velocity for projectile motion?
Replies
25
Views
2K
Bead on a rod which is being pulled by an ideal string with velocity v
Replies
27
Views
323
I Force problem - how the force interacts with time
Replies
2
Views
1K
A Bernoulli, lift and cause & effect
Replies
30
Views
3K
I Energy Released From Dropping Things Onto Neutron Stars
Replies
20
Views
2K
Why can we move the spring with constant speed when we apply a force?
Replies
29
Views
2K
I Work in hydrostatic system in cylinder with piston: P_int or P_ext?
Replies
5
Views
988

Hot Threads

Recent Insights

Back
Top