Block on inclined plane - pushing vs pulling

In summary, when pushing or pulling with the same amount of force, the vertical force is sin (alpha) * P in the same direction, but when pushing or pulling with different amount of force the vertical force is sin (alpha) * P in the opposite direction.
  • #1
mdavis501
1
0
When resolving all of the VERTICAL forces in a block that is being pushed up an incline with some incline amount theta, then when PUSHING with force P at an angle of alpha on the block, then the vertical component of force P is sin (alpha) * P in the downward direction (opposite of the Normal force); however, when pulling the block UP the incline with same alpha and same force P, then the vertical force is sin (alpha) * P upwards in the SAME direction as the normal force N. In both cases friction is in the direction of DOWN the incline. In both cases the Parallel and Perpendicular forces of gravity are the same. So, it would seem that the force P needed to push the block will be different than the force necessary to pull the block. Then seems counter-intuitive. Am I thinking correctly here?
 
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  • #2
It only makes sense to speak of an angle relative to something.

If the pushing and pulling are truly in the same direction, then there will be no difference at all.
 
  • #3
I don't understand what the point of the incline is. You have the same thing on level ground: Pulling forward & up reduces the normal force, and thus friction. Pushing forward & down increases friction.
 
  • #4
A.T. said:
I don't understand what the point of the incline is. You have the same thing on level ground: Pulling forward & up reduces the normal force, and thus friction. Pushing forward & down increases friction.

You could imagine that the object is pulled by a rope attached to the center of the forward face. Since the rope will be taut under tension, it acts just like a stiff wire would under tension. The most likely direction to pull something up an inclined plane is to pull parallel with the incline. In other words, the rope/wire aims up, the handhold having the same distance from the inclined slope as it does at the attachment point. So one is lifting as one also pulls forward in this case.

Now imagine pushing the object up the slope with a stiff wire since the rope would collapse under compression. The wire is again attached to the center of a face, but the rear face this time. The most likely direction of the wire is again parallel with the incline. In this case one is pushing up (not down) as one pushes forward.

The rope (or stiff wire) can be quite short, but the push/pull efforts are still both parallel with the slope, even until they are infinately short. The two cases of friction are now identical.

Wes
...
 
  • #5
Wes Tausend said:
The most likely direction to pull something up an inclined plane is to pull parallel with the incline.
OK, I misunderstood that it's about pulling/pushing at an angle to the surface. When parallel then both are the same.
 

Related to Block on inclined plane - pushing vs pulling

1. How does the force required to push a block up an inclined plane compare to the force required to pull it?

The force required to push a block up an inclined plane is greater than the force required to pull it. This is because when pushing, the force must overcome both the weight of the block and the force of friction between the block and the surface of the inclined plane.

2. Does the angle of the inclined plane affect the force required to push or pull a block?

Yes, the angle of the inclined plane does affect the force required to push or pull a block. As the angle of the inclined plane increases, the force required to push or pull the block also increases. This is because the steeper the angle, the greater the component of the force of gravity acting against the motion of the block.

3. Can the force required to push or pull a block up an inclined plane be calculated?

Yes, the force required to push or pull a block up an inclined plane can be calculated using the formula F = mg(sinθ + μcosθ), where F is the force required, m is the mass of the block, g is the acceleration due to gravity, θ is the angle of the inclined plane, and μ is the coefficient of friction between the block and the surface of the inclined plane.

4. How does the coefficient of friction affect the force required to push or pull a block up an inclined plane?

The coefficient of friction affects the force required to push or pull a block up an inclined plane by increasing the force needed to overcome the friction between the block and the surface of the inclined plane. A higher coefficient of friction means a greater force is needed to push or pull the block.

5. What other factors besides the angle of the inclined plane and coefficient of friction can affect the force required to push or pull a block?

Other factors that can affect the force required to push or pull a block up an inclined plane include the mass of the block, the presence of any external forces acting on the block, and the type of surface the block is resting on. For example, a rough surface will have a higher coefficient of friction and require a greater force to move the block compared to a smooth surface.

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