Laws of Motion in weight lifting

In summary, The conversation discusses the application of Newton's laws to a bench press exercise and how to understand the forces involved during the eccentric phase. The main question is how to explain the downward movement of a dumbbell despite the fact that the forces seem to be equal. It is explained that to start the downward motion, the upward force must be decreased momentarily to allow gravity to pull it down. The concept of inertia is also mentioned, with the understanding that there must be a net upward force to decelerate the dumbbell.
  • #1
SPYDER2002
2
0
Hi all, I'm trying to get my head round how to apply Newtons laws and an exercise like a bench press, probably a bit simple to what you guys are used to.

I want to make it as simple as possible to understand what forces would be acting during the eccentric phase of an exercise, I.e lowering the barbell during a bench press.

Rather than viewing it as a moment I want to view it as an object moving vertically at a constant speed. So say you lower a 50K dumbell over a 3 second period, let's suppose you move it 0.6 metres. means it's traveling at 0.2 m/s
now if it's moving at a constant speed, the forces should be equal, which means you'd be pushing up at 50K, but if that was the case, how would it be lowering in the first place. THink I'm just looking at it from the wrong angle. Anyways any help would be really appreciated, if anyone would be willing to chat on MSN it would be much appreciated.


Regards
Zach.
 
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  • #2
Say it's stationary at the top. So you are pushing it up with 50k, and gravity is pulling down with 50k. To start it moving down, you momentarily decrease the force with which you are pushing it up, so that gravity can pull it down. It accelerates downwards. It stops accelerating, and continues moving downwards with constant velocity when you increase your upward force back to 50k.
 
  • #3
Cool, that makes sense, then because of the intertia, a force greater than 50K would be required at the bottom of the motion to stop it.

Thanks for your help.
 
  • #4
SPYDER2002 said:
Cool, that makes sense, then because of the intertia, a force greater than 50K would be required at the bottom of the motion to stop it.

Thanks for your help.

What do you mean "because of the inertia?" Be careful not to misuse terminology.

The only thing inertia does is tell you that if you don't do something, the weight will keep moving downward at a constant speed. I.e., there has to be a *net* upward force on the dumbbell if you want to decelerate it. Obviously you have to push up with more than 50 kg * g if you want there to be a *net* force.
 

1. What are the three laws of motion in weight lifting?

The three laws of motion in weight lifting are: 1) the law of inertia, stating that an object at rest will remain at rest and an object in motion will remain in motion unless acted upon by an external force; 2) the law of acceleration, stating that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass; and 3) the law of action and reaction, stating that for every action, there is an equal and opposite reaction.

2. How do the laws of motion apply to weight lifting?

The laws of motion apply to weight lifting in several ways. First, the law of inertia explains why it is difficult to move heavy weights, as they have a greater mass and therefore require more force to accelerate. Second, the law of acceleration explains how muscles must exert a greater force to lift heavier weights. Finally, the law of action and reaction explains how the force exerted by the muscles on the weights will result in an equal and opposite force exerted by the weights on the muscles.

3. How can we use the laws of motion to improve our weight lifting technique?

By understanding the laws of motion, we can improve our weight lifting technique by applying the correct amount of force and acceleration to lift the weight efficiently. This means using proper form and technique to minimize wasted energy and maximize the force applied to the weight. Additionally, understanding the law of action and reaction can help us anticipate and counteract any potential injuries caused by the weights pushing back on our muscles.

4. Do the laws of motion only apply to traditional weight lifting exercises?

No, the laws of motion apply to all forms of weight lifting, including traditional exercises such as bench press and squats, as well as more dynamic exercises like Olympic lifts and plyometrics. These laws also apply to movements outside of weight lifting, such as throwing or pushing objects, as they all involve the application of force to move an object.

5. What role do the laws of motion play in determining the amount of weight we can lift?

The laws of motion play a crucial role in determining the amount of weight we can lift. As mentioned earlier, the law of inertia explains why it is difficult to move heavier weights, while the law of acceleration explains why we need to exert more force to lift heavier weights. Additionally, our muscle strength and coordination also play a role, as they determine how efficiently we can apply force and accelerate the weight. By understanding and applying the laws of motion, we can work towards increasing our strength and improving our lifting capacity.

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