Force vs Weight: Which is Heavier?

  • Context: High School 
  • Thread starter Thread starter havechanged
  • Start date Start date
  • Tags Tags
    Force Weight
Click For Summary

Discussion Overview

The discussion revolves around the question of how the weight registered by a scale changes based on the behavior of flies inside a capped jar. Participants explore the concepts of mass, weight, and the forces involved when the flies are either sitting still or flying within the jar.

Discussion Character

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

Main Points Raised

  • Some participants propose that the weight of the jar remains constant regardless of whether the flies are sitting or flying, as the mass of the jar and flies combined does not change.
  • Others argue that the force exerted on the scale includes contributions from the jar, the air, and the flies, suggesting that the weight registered should be the same in both scenarios.
  • A participant notes that if the flies perform a collective motion, such as diving to the bottom, the scale may momentarily register a lighter weight.
  • One participant introduces an analogy with a fish in water, stating that the weight applied to the scale remains constant regardless of the fish's position in the water.
  • Another participant mentions that if the flies are accelerating upwards, the scale will register the highest value, implying that acceleration affects the weight measurement.
  • A later reply questions the implications of the flies accelerating downwards, indicating that the discussion includes considerations of dynamic forces.

Areas of Agreement / Disagreement

Participants generally agree that the weight of the jar with the flies should remain constant under normal circumstances, but there are competing views regarding the effects of acceleration and the behavior of the flies on the scale's reading.

Contextual Notes

There are unresolved aspects regarding the effects of acceleration and the potential fluctuations in weight measurement due to the flies' movements. The discussion does not reach a consensus on how these factors influence the overall weight registered by the scale.

Who May Find This Useful

This discussion may be of interest to those exploring concepts of force, weight, and dynamics in physics, particularly in relation to systems involving multiple interacting components.

havechanged
Messages
21
Reaction score
0
Hey!

Okay, there are a bunch of flies in a capped jar. You place the jar on a scale. The scale will register the most weight when the flies are:

A. sitting on the bottom of the jar.

B. flying around inside the jar.

C. weight of the jar is the same in both cases.


I can't organize my thoughts! I can't explain this.

Any help will be greatly appreciated!
 
Physics news on Phys.org
C.

The flies are suspended in air, the air forces down on the jar. That's assuming the flies are not performing some collective motion. For example, if they all suddenly dive to the bottom, the jar will be momentarily lighter, regaining normal weight when they land.
 
Yeah, that is what I was thinking...it is just driving me crazy because I can't collect my thoughts as to the "scientific" reason this is so. Hmm...thanks though!
 
Well, for a scientific reason, think about this. The mass of the jar (which includes the flies inside of it) does not change depending on the location of the flies. Unless they perform some act like krab said.
 
Agreed. The answer, without special circumstances, is C.
 
Originally posted by havechanged
Hey!

Okay, there are a bunch of flies in a capped jar. You place the jar on a scale. The scale will register the most weight when the flies are:

A. sitting on the bottom of the jar.

B. flying around inside the jar.

C. weight of the jar is the same in both cases.


I can't organize my thoughts! I can't explain this.

Any help will be greatly appreciated!

First, if you consider the MASS "jar+flies", that is definitely a constant whatever the flies are doing: sitting or flying.

Now, if you consider the weight of the "jar+flies", that means you are looking at force that is exerced on the scale. There is there tree contribution to that force: from the jar (constant force), from the air in the jar and from the flies in the jar. Now do not forget that the flies rely on the air to be able to fly. Therefore, whether they sit on the bottom or they fly should not make any difference. In the air, the wings of the a fly exert on average a force on the air which is transmitted to the bottom of the jar and therefore to the scale. If there was no air (vaccum), the fly could simply not fly and would always rest at the bottom.

An easier picture would be to consider the jar filled with water whith a fish swiming in the jar. It would not matter if the fish float at the surface, sit a the bottom or swim in the middle: the fish weight applies a force on the water which is transmitted to the bottom of the jar.

Note: you may find that the force is not always constant in time and that the force is fluctuating during the measurement. That is because when the fish/flies move around they exert additional forces necessary to accelerate/decelerate their motions. However, these fluctuation should average to zero and the average weight in time should be "jar+air/water+flies/fish". Think that it is the same when you try to measure your own weight on a scale but you do not stay still...
 
If the flies are all accelerating upwards, the jar will register the highest value.
 
Originally posted by FZ+
If the flies are all accelerating upwards, the jar will register the highest value.

And if they are accelerating downwords - stooping ?
 

Similar threads

High School The Effect of Linear and Rotational Motion on Measured Weight
  • · Replies 10 ·
Replies
10
Views
2K
High School How does the weight on a scale change when an object is submerged in water?
  • · Replies 35 ·
2
Replies
35
Views
5K
High School Will the weight of jar changed?
  • · Replies 4 ·
Replies
4
Views
8K
High School Question: Helicopter over a scale
  • · Replies 4 ·
Replies
4
Views
1K
High School Calculate needed dimensions of table - Center of mass, levers etc
  • · Replies 11 ·
Replies
11
Views
3K
High School What Is Mass and How Is It Defined in Physics?
  • · Replies 23 ·
Replies
23
Views
3K
High School Why does friction decrease with repeated force application?
  • · Replies 11 ·
Replies
11
Views
3K
How Do You Build a Functional Leyden Jar for a School Project?
  • · Replies 3 ·
Replies
3
Views
3K
High School Help Scaling Gravity Simulation
  • · Replies 7 ·
Replies
7
Views
3K
Undergrad Why do objects fall at the same speed in free fall?
  • · Replies 30 ·
2
Replies
30
Views
6K