Math Is Fun Forum

sakif1

Member

From: Bangladesh

Registered: 2015-02-05

Posts: 3

I need a formula

If I pick a weight of 1 newton by a 1 foot long stick. Then how much force I need to pick that weight?
And which formula I need to use here?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: I need a formula

hi sakif1

Welcome to the forum.

Are you hoping to use a lever to raise the weight ?  If so then you need to know the distances from the 'fulcrum' to the hand and to the weight.

If you're just hoping to raise the weight by twisting your wrist, then it's even more complicated because you would have to know the exact size of your hand and which muscles were doing the lifting. 

Maybe what you are after is the torque which is weight times distance.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

sakif1

Member

From: Bangladesh

Registered: 2015-02-05

Posts: 3

Re: I need a formula

Actually, I really want to know....
If i pick a Dumbell using the common style you must know.
If i pick the dumbell using 98j. Then how much j my body really using if the is dumbell 1 foot far from my muscle (bycep)?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: I need a formula

hi sakif1

OK, I've made a diagram.

The fulcrum is the point at your elbow where your arm bends.

A turning 'moment' is calculated by multiplying the weight by the perpendicular distance to the fulcrum.

So here the distance for the weight is given letter c, and the distance for your biceps is given letter d.

To lift the weight w.c = f.d

So f = w.c/d

There are a number of practical problems with arriving at an answer.

Firstly you need to estimate c and d.  As you bend your arm, c will get less so the lift becomes easier.  It doesn't matter if you want to use inches rather than cm, as long as you use the same units for both.

w needs to be measured in Newtons not Joules.  If you know the mass (m) (eg. 10 Kg) then you can get w by w = mg where g is the acceleration due to gravity.  Given all the potential inaccuracies in this, you might as well take g = 10.

Finding the correct point for measuring d will be difficult as the muscle attaches somewhere inside your arm and hence out of sight.  The shorter d is, then greater f would have to be and a small error in estimating d will cause a large error in your calculation.

The final value will be measured in Newtons.

Happy weight lifting! 

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob