I had a conversation with a friend and it inspired me to the following
problem:

A guy and gal are dating. The gal is sensitive about her weight,
and so she has never revealed just how much she weighs to her
boyfriend. Ofcourse, the boyfriend is very curious, but he can't
get the information from her doctor, her, or her friends. So the
guy turns to you for some help.

Is there an experiment that can be performed on the girl to measure
her weight (say within 10 pounds) without her knowing or without using
a weight scale directly? Assume she isn't a physics major, and, has
some commonsense to decline your invitation to ride a see-saw.

Any solution would be great, but I would prefer ones that are simple and
cheap, instead of ones requiring some sort of James Bond weighing device,
like replacing a floor tile with a secret weighing device that uses
piezoelectric material.

I may possibly have two simple and cheap solutions, but since I don't want
to influence your answer, I'll post my solution later.

thanks and enjoy!

"FreddyFoobar" wrote in message
om...

Is there an experiment that can be performed on the girl to measure
her weight (say within 10 pounds) without her knowing or without using
a weight scale directly? Assume she isn't a physics major, and, has
some commonsense to decline your invitation to ride a see-saw.

Get her into a rectangular bathtub naked. Make up some excuse to dunk her
into the water. Measure the volume of displaced water using an elaborate
system of lines etched into the tub walls. Calculate her weight assuming an
average body density of 1.1 g/cm3.

"Brian" wrote in message
...

"FreddyFoobar" wrote in message
om...

Is there an experiment that can be performed on the girl to measure
her weight (say within 10 pounds) without her knowing or without using
a weight scale directly? Assume she isn't a physics major, and, has
some commonsense to decline your invitation to ride a see-saw.

Get her into a rectangular bathtub naked. Make up some excuse to dunk her
into the water. Measure the volume of displaced water using an elaborate
system of lines etched into the tub walls. Calculate her weight assuming
an
average body density of 1.1 g/cm3.


Get a more accurate reading by putting her in a boat in the bath. She'll
displace her weight and you won't have to hold her under the water. Cons -
The size of the boat and/or the bath may need to a be a little different to
those normally encountered, and I can't think what you'd use as an excuse.

Or, take the car to a weighbridge with her in it (for fun), then secretly go
back without her.

In message , Martin Stone
writes
"Brian" wrote in message
...

"FreddyFoobar" wrote in message
om...

Is there an experiment that can be performed on the girl to measure
her weight (say within 10 pounds) without her knowing or without using
a weight scale directly? Assume she isn't a physics major, and, has
some commonsense to decline your invitation to ride a see-saw.

Get her into a rectangular bathtub naked. Make up some excuse to dunk her
into the water. Measure the volume of displaced water using an elaborate
system of lines etched into the tub walls. Calculate her weight assuming
an
average body density of 1.1 g/cm3.


Get a more accurate reading by putting her in a boat in the bath. She'll
displace her weight and you won't have to hold her under the water. Cons -
The size of the boat and/or the bath may need to a be a little different to
those normally encountered, and I can't think what you'd use as an excuse.

Use lots of bath salts, so she floats _without_ the boat.

Inventing an excuse for that is left as an exercise for the reader.

"FreddyFoobar" wrote in message
om...

Is there an experiment that can be performed on the girl to measure
her weight (say within 10 pounds) without her knowing or without using
a weight scale directly? Assume she isn't a physics major, and, has
some commonsense to decline your invitation to ride a see-saw.

Take a stroll through the park. Offer to push her on the swing.
Time the period of oscillation.

"Martin Stone" wrote in message ...
"Brian" wrote in message
...

"FreddyFoobar" wrote in message
om...

Is there an experiment that can be performed on the girl to measure
her weight (say within 10 pounds) without her knowing or without using
a weight scale directly? Assume she isn't a physics major, and, has
some commonsense to decline your invitation to ride a see-saw.

Or, take the car to a weighbridge with her in it (for fun), then secretly go
back without her.

I thought about this one. It was one of my first thoughts. Ofcourse,
it would be a very good solution to the problem, but I'm not sure about
the resolution of those weighbridges. Considering that they are usually
used to weight heavy trucks, I think they have a resolution of 1/10 of
a ton?

So, you may be able to narrow her weight down to a 200lb range.
Hopefully for the boyfriend's sake, and the girl's health too, she's
not so big that 100lbs off is reasonable experimental error!

"Greg Neill" wrote in message
...
"FreddyFoobar" wrote in message
om...

Is there an experiment that can be performed on the girl to measure
her weight (say within 10 pounds) without her knowing or without using
a weight scale directly? Assume she isn't a physics major, and, has
some commonsense to decline your invitation to ride a see-saw.

Take a stroll through the park. Offer to push her on the swing.
Time the period of oscillation.


This is a physics newsgroup, right?

Just checking.

Drive over the mill scale at the elevator befor and after you pick her
up .
But if you nead a scale or must over inflate the rubber on the riders
side ,,, dont buy her 4 big macs and a diet coke , buy here a bus
ticket instead.
No live stock please . bumper sticker

"Greg Neill" wrote in message .. .
"FreddyFoobar" wrote in message
om...

Is there an experiment that can be performed on the girl to measure
her weight (say within 10 pounds) without her knowing or without using
a weight scale directly? Assume she isn't a physics major, and, has
some commonsense to decline your invitation to ride a see-saw.

Take a stroll through the park. Offer to push her on the swing.
Time the period of oscillation.

I thought about the swing problem too, but I thought the period of
oscillation depends only on the length of the 'string' and not on
weight/mass?

Anyways, you are in the right park (hint, hint) I'll post
my -possible- solution to the problem soon.