How can I lift more than my weight?

  • Context: Undergrad 
  • Thread starter Thread starter Guni22
  • Start date Start date
  • Tags Tags
    Lift Weight
Click For Summary

Discussion Overview

The discussion centers around the mechanics of using a tricep machine, specifically how it is possible to lift weights greater than one's body weight through the use of pulleys and levers. Participants explore the principles of mechanical advantage and the forces involved in this type of exercise equipment.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes a tricep machine that uses a pulley system, questioning how they can lift more weight than their own body weight.
  • Another participant explains that machines often utilize levers and pulleys to reduce the force needed to lift weights, suggesting that the pulley configuration can halve the force required.
  • A different participant notes that the torque around the elbow is relevant to the mechanics of the tricep machine, indicating that the direction of force does not lead to being lifted off the seat.
  • One participant shares their personal experience of lifting a weight greater than their mass, expressing surprise and seeking clarification on how pulleys facilitate this capability.
  • Another participant elaborates on the mechanics of tension in the cable system, explaining that the tension is doubled due to the configuration of the cable runs, which allows for lifting heavier weights with less force.
  • A later reply discusses the concept of work and mechanical advantage, referencing Archimedes and the principle that less force can be used over a longer distance to accomplish the same work.

Areas of Agreement / Disagreement

Participants express various viewpoints on the mechanics of the tricep machine and the role of pulleys, with some agreeing on the principles of mechanical advantage while others raise questions about specific configurations and their effects. The discussion remains unresolved regarding the exact mechanics of different machine types.

Contextual Notes

Some participants mention the presence of friction in the machines, which may affect the overall force required to lift weights. There are also references to different pulley configurations that may lead to varying mechanical advantages, indicating a need for clarity on specific machine designs.

Guni22
Messages
7
Reaction score
0
There is a tricep machine which is basically a pulley, with some rope connected to a stack of weights and a bar for you to push down on using your triceps on the other end of the rope.

How is it possible that if I'm 140 pounds, I can lift like 180 or more on that machine? If I want to want the weight of 180 pounds, then I must apply more than 180 pounds of force on the bar. But if I only weigh 140 pounds, won't I just be lifted up off the floor? I thought that I could resolve this by thinking that maybe I was just transferring the gravity of my body onto the bar, but my muscles are providing extra force, but isn't that just an internal force?
 
Physics news on Phys.org
Usually machines don't have you apply the amount of force that gets lifted up. There's levers and pulleys (as you mentioned) which greatly reduce the force you need to lift the weight.

Just placing the pulley on top of the weights would half the force you need to apply. And there's probably other mechanical advantages as well.

180lbs is a lot of weight to lift with just your triceps.

Can you find a picture of a similar machine by any chance?
 
For a tricep machine, there is a torque around your elbow, not a vertical lifting force applied at your center of gravity (unlike the lat machine) -- and the torque is in the wrong direction to lift you off your seat!
 
Last edited:
Guni22 said:
There is a tricep machine which is basically a pulley, with some rope connected to a stack of weights and a bar for you to push down on using your triceps on the other end of the rope.
There are two of these machines at local cetner I go to. One uses a pulley at the weight stack, and the force you apply is 1/2 the weight selected. The other is connected directly to the weight stack and the force you apply is equal to the weight selected. There is a second pulley overhead, but that doesn't reduce the force. Since you'd be lifted off the ground trying to push down 180 lbs, it must be the type where you apply 1/2 the force of the selected weight stack.

russ_watters said:
For a tricep machine ... torque is in the wrong direction.
That would be a bicep machine (pulling up instead of pushing down).
 
Last edited:
I also found this strange, 1 week ago I tried to lift 70 kg (my mass is 75 kg) with the triceps machine and I could do it easily. I thought that with all the friction (I can hear it, I guess the machine needs some oil somewhere) and I don't feel like my mass is only 5 kg when I lift the weight, I was really astonished.
Can someone explain me how a pulley can help you to lift up to twice your mass? I know it looks like a problem of introductory physics but I'm still surprised of the result. Anyway that would explain why it's so easy to lift up a lot of weight with this machine rather than with an iron bar.
 
fluidistic said:
Can someone explain me how a pulley can help you to lift up to twice your mass?
You generate a tension on the cable by pushing down on the bar connected to the cable, and that tension remains the same through out the cable back to it's connection point (ignoring friction). At the weight stack with the pulley, there are two runs of the cable going to the weight stack, down from the connection point to the pulley, then back up to the upper pulley. Since there are two runs of the cable lifting the weight, the upwards force from the cable is double the tension. If the weight stack isn't accelerating, then the tension is 1/2 the weight of the weight stack.
 
Last edited:
Work is force times distance. If you increase the distance over which you apply a force, you can do the same work with a smaller force. This is the principle behind pulleys, levers, ramps, screws, and gears. You use less force but over a longer time to accomplish the same work. It's called "Mechanical Advantage". Archimedes was one of the first ones to exploit this. He famously said, "Give me a place to stand and with a lever I will move the whole world." He also purportedly stunned King Hiero of Syracuse, by lifting a three mast ship out of the water by himself using ropes and pulleys.
 

Similar threads

Undergrad 1:1 versus 2:1 Mechanical Advantage debate
  • · Replies 20 ·
Replies
20
Views
2K
High School Can I hold down more than my body weight on a 1 to 1 system?
  • · Replies 13 ·
Replies
13
Views
3K
Undergrad Car top boat loader: What is the lifting weight?
  • · Replies 9 ·
Replies
9
Views
2K
High School How much weight am I lifting when I pick up one end of a canoe?
  • · Replies 4 ·
Replies
4
Views
4K
Undergrad Calculating actual weight lifted on a pulley weight machine
  • · Replies 14 ·
Replies
14
Views
19K
Undergrad Bicycle front tire wobble due to weight on the back of the bike
  • · Replies 21 ·
Replies
21
Views
5K
High School Pulley Carrying Capacity: Can It Handle 150 lbs?
  • · Replies 9 ·
Replies
9
Views
3K
High School Lifting an object with a mass difference of just 1kg
  • · Replies 6 ·
Replies
6
Views
1K
Undergrad How to control the weight of an object?
  • · Replies 23 ·
Replies
23
Views
5K
Undergrad Calculating Force, Work, and Power Values For A Lifting Movement
  • · Replies 16 ·
Replies
16
Views
18K