# Hourglass on a balance scale

• B
• DrDavy
In summary, a balance scale with two spent hourglasses that weigh exactly the same will tilt towards the flipped hourglass after briefly rising while the sand begins to descend. This is due to the weightlessness of the falling sand and the additional impact force from the momentum change when it hits the base. This has been confirmed by an actual experiment and can be recreated at home for further exploration.

#### DrDavy

Here's my question:

Two spent hourglasses that weigh exactly the same on a balance scale. You flip one over so that it's running. What happens to the balance?

First, welcome to PF!

As to the question, what do you think will happen and why?

berkeman
I think the scale tilts to the flipped slide after first very briefly rising while the sand begins to descend. While the sand is falling it’s weightless( causing it to slightly rise), but upon impacting the base the falling sand would impart its weight plus an additional impact force from the momentum change and start tilting in the opposite direction. That’s my guess.

vanhees71 and Lnewqban
Here is data from an actual experiment of an hourglass on a scale.

Last edited:
vanhees71, Lord Jestocost, OmCheeto and 3 others
Before I look at the spoiler, I want to say that I think the one that is running would be lighter, because at any given moment, there would be grains of sand in the air. I guess that's the point of the first part of Erobz's answer. I'm not smart enough to grasp the second part of that answer.

berkeman and bob012345
Thank you very much, bob012345, for the definitive answer!

bob012345
DrDavy said:
Thank you very much, bob012345, for the definitive answer!
You're welcome. You might enjoy setting up a 'kitchen' experiment to play with this situation.

## What is an hourglass on a balance scale?

An hourglass on a balance scale is a physical demonstration of the concept of equilibrium, where two opposing forces are equal and balanced. The hourglass represents time and the balance scale represents weight or mass.

## How does an hourglass on a balance scale work?

The hourglass on a balance scale works by demonstrating the principle of moments, where the weight of the sand in the hourglass creates a downward force on one side of the scale, while the weight of the hourglass itself creates an equal and opposite upward force on the other side of the scale. When these two forces are balanced, the hourglass remains in a state of equilibrium.

## What factors can affect the balance of an hourglass on a balance scale?

The balance of an hourglass on a balance scale can be affected by various factors such as the weight of the hourglass, the amount of sand in the hourglass, the length of the hourglass, and the distance between the two sides of the balance scale. Any change in these factors can disrupt the equilibrium and cause the hourglass to tip to one side.

## What does an hourglass on a balance scale represent?

An hourglass on a balance scale represents the balance between time and weight or mass. It also serves as a visual representation of the concept of equilibrium, where two opposing forces are equal and balanced.

## What is the significance of an hourglass on a balance scale?

An hourglass on a balance scale is significant as it demonstrates the laws of physics and the concept of equilibrium in a simple and tangible way. It also serves as a reminder of the importance of balance and the constant passing of time in our lives.

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