Jan 14th 2016  


FWC Instructor Dave Courtney Jones performing a standing jump

This entry is part 5 of 11 in the series Training challenges

Earthbound beings that we are, our hinge-like joints and large leg muscles allow us to defy gravity and reach new heights. In theory. Once we leave childhood behind, most of us stick to the earth as though it is a mark of adulthood.  But among us there are secret jumpers, people who try to rediscover the joy of transient weightlessness.

Here is one of them.

“A confession.

Er, hi.

My name is Dave, and I’m forty-four. And a quarter.

FWC Instructor Dave Courtney Jones jumps onto a table

So, the thing is…

You promise you won’t judge me?

The thing is, recently I’ve taken to jumping. Not the ordinary kind of jumping.

I’ve started doing standing jumps onto a table.

I do jumps with ankle weights.

I do squat thrusts, followed by jumps onto a bench about a metre away.

I do jumps onto one leg.

I do forward jumps, backward jumps, sideways jumps and spinning jumps.FWC Instructor Dave Courtney Jones jumps onto a table

I do jumps in the dark, and jumps in the rain, and sometimes when it’s dark and raining. Although not exclusively.

Oh yes. And I jump with Classical Chinese weapons. That’s not weird.

And this is not a mid-life crisis. Oh, no!

You see, I know I need to learn to jump, because Dennis told me that I need to learn to jump.

(And anyway, I don’t reach “mid-life” until next September.)

In fact he told me twice. Recently. Not twenty years ago.

He might tell me one more time, but there probably won’t be a fourth. Anyway, I’m hoping he won’t need to.FWC Instructor Dave Courtney Jones jumps onto a table

He also told me I needed to be light. And he even said that it didn’t mean I had to lose (more) weight. Although, if I’m completely honest with myself, that would probably help too.

Just to cover all the bases, I’m also strengthening my thighs. And my core. I’m bouncing on my knuckles. I’m doing body bridge. I’m using kettle bells. I’m even hula hooping.

I had never, ever tried to jump onto a table before December 2015. But – amazingly – I could do it first time. It was more about belief and willpower than anything else.

But the best thing about all this jumping? It’s amazing fun, and my body feels a LOT younger.

The end result? To be seen in a pattern near you next year!”

E=MC² – sorry, wrong equation, but there’s gravity in there somewhere…

Whilst Dave was owning up to being a secret jumper, it was just before Christmas and we were having a discussion about how much effort it would take to reduce the gravitational pull caused by the excesses of one day of traditional British FWC Instructor Dave Courtney Jones jumps onto a tableChristmas food.

Not wishing to dwell on it we turned to Dave. “So how much power does it take to lift you onto the table?” We thought we should be able to work that out, Dave being a Chartered Engineer and me having O level maths (GCSE in new money).

And now the science bit (including the right sort of gravity)

After taking some measurements, Dave did some quick and simple calculations:

“How much energy does it take to jump onto a table? In basic terms, this can be thought of as the potential energy gained.

Potential energy = mass x gravity x heightFWC Instructor Dave Courtney Jones jumps onto a table

My mass 93kg (including uniform and ankle weights – promise!)

Gravity = 9.81 m/s²

Height (of table) = 0.7m

So potential energy of jump = 93kg  x 9.81m/s² x 0.7m = 638.631 Joules

Which is 0.639 kJ which is 0.15272466539kcal.  I’m not sure that’s even a rice krispie never mind a bite of mince pie.  And I put all the numbers in to allow you a few more molecules of food.FWC Instructor Dave Courtney Jones jumps onto a table

How much power? Well, it takes roughly a quarter of a second to produce the spring which lifts me onto the table.

Power = energy / time = 639J / 0.25s = 2,556W = 2.556kW or (which sounds more impressive) 3.4 British Horsepower”

Compare this to the 350kW output of the Porsche Carrera GT3 and decide which is more impressive (and better for the planet?).

Hmmm, are you sure that’s correct?

Yes we know that we have used gravitational potential energy calculations to give us a rough idea of power. Dave was not up for having the elastic potential energy of his leg muscles tested though I tried to assure him that we could get them refitted.  If you have any ideas for how we could do this (apparently elite high jumpers have it done) then get in touch with Dave.  In the meantime, he’s still jumping.

PS All the photos in the jump sequence are from one jump.