Finding Mass of Wooden Block Without Masing It

In summary, the conversation discusses various methods for finding the mass of a wooden block without directly measuring it. Suggestions include using Archimedes' principle and the buoyant force of water, measuring the object's weight on a scale, and using a spring scale to measure the force of gravity. It is eventually suggested to float the object in a container of water and measure the amount of water that overflows, which reveals the mass of the object.
  • #1
Riogho
119
0

Homework Statement


Okay, my chemistry teacher has given each of us an object, my object is a wooden block. We are required to find the mass of this object, WITHOUT massing the object. He has given us no procedure as we must go on simply our knowledge. Or yours :D


Homework Equations


Possibly F=ma


The Attempt at a Solution



The only solution I can come up with, is to drop the wood block from a certain height and and measure how long it takes to fall to the ground, find the acceleration, and use the graviational constant as the force. Unfortunately, unless I drop this from a great height, and have awesome reflexes, getting any accuracy will be difficult with my wristwatch. I was wondering if anyone else had any ideas.
 
Physics news on Phys.org
  • #2
How about putting the object in a liquid of known density (i.e., water)? From this you can measure the amount of the object that's submerged, or if it's all submerged, how far below the surface the object floats, and consequently the mass of the object.
 
  • #3
What ARE you allowed to measure?

You can weigh the object on a scale (not a balance). Technically, that is not massing the object since you are measuring weight (the force of gravity) rather than mass. Weight also depends on gravity. A scale wouldn't work the same on the moon, but a triple-beam-balance would.

It may not be what your teacher had in mind, but it is a valid solution to the exact problem your teacher gave
 
  • #4
Dropping the block from a certain height is a poor solution, since the time it takes to reach the ground is INDEPENDENT of mass (unless you count for air resistance, and know the aerodynamic properties of wood and how they relate to mass)
 
  • #5
chickendude said:
What ARE you allowed to measure?

You can weigh the object on a scale (not a balance). Technically, that is not massing the object since you are measuring weight (the force of gravity) rather than mass. Weight also depends on gravity. A scale wouldn't work the same on the moon, but a triple-beam-balance would.

It may not be what your teacher had in mind, but it is a valid solution to the exact problem your teacher gave

Using a scale with predetermined masses on one side is the same as using a balance...
 
  • #6
We can't mass the object :P

We have to use something else to find it. I don't know the equations for density to find mass though :P
 
  • #7
Density = mass/volume... Have you done buoyant forces yet?
 
  • #8
Nope :P

How would I go about checking how far it is submerged and how will that tell me what the wood blocks density is?

Because I'll need an exact density to find the mass, volume will not be hard though.
 
  • #9
There's also the option of attaching the block to a spring and measuring how far from the equilibrium position the block stretches it...

To use the water method you'll have to either a)measure how much of the block is underwater (just measure how high up on the block the water level reaches) or b) if the block is completely submerged measure how far from the surface the bottom of the object is.

When the object is at rest, either fully or partially submerged, we know that the net-force acting on the object is zero. The only 2 vertical forces acting on the object is the buoyant force of the water and gravity; therefore, if we know the magnitude of the buoyant force, we know the weight of the object.
For an object completely submerged, use Archimedes' principle that the buoyant force acting on an object at a specific depth is a force of magnitude equal to the weight of the water that has been displaced by the object; that is
Buoyant Force = (mass of water displaced) x g = (volume of water displaced) x (density of water) x g

Once you've calculated the buoyant force acting on the object, the weight, and therefore mass, are easily found.
 
  • #10
But my idea wouldn't work?

I always thought you could find the graviational mass = intertial mass, and wala- you got mass

b60b9c412aea5353f79f39d7d1df152d.png
 
  • #11
What was your idea? Measuring the object's speed? in free-fall won't tell you anything about the mass of the object.
 
  • #12
Why not?
 
  • #13
If you do use the water method, don't forget to include the atm pressure in the room and, if the object is submerged, the water pressure pushing down on the object from the top (which is found using the same method as finding the buoyant force).
 
  • #14
Because acceleration due to gravity is independent of mass.
 
  • #15
But it has to do with inertia doesn't it?
 
  • #16
Why don't you simply weigh the object?

Weighing is not the same as massing. For example: use a spring scale. You are measuring the force of gravity by seeing how far it stretches the spring.and, dropping it wouldn't work because the acceleration of gravity is 9.8 m/s^2 regardless of the mass, so it wouldn't tell you anything about the mass.
 
  • #17
I guess the teacher has told you the answer already – but here goes anyway

Float your wooden object in a container full to the brim with water. Weigh the water which overflows. Bingo
 

1. How can I find the mass of a wooden block without weighing it?

One way to find the mass of a wooden block without weighing it is by using its dimensions and density. You can measure the length, width, and height of the block and then calculate its volume by multiplying these values. Next, find the density of the type of wood the block is made of and multiply it by the volume to get the mass.

2. Can I use a ruler to measure the dimensions of the wooden block?

Yes, you can use a ruler to measure the dimensions of the wooden block. Make sure to measure the length, width, and height of the block accurately to get the most precise results.

3. How do I determine the density of the wooden block?

You can determine the density of the wooden block by dividing its mass by its volume. You can either measure the mass with a scale or calculate it using the dimensions and the density formula. The density of different types of wood can also be found online or in reference books.

4. Is it necessary to know the type of wood in order to find the mass?

Yes, it is necessary to know the type of wood to accurately find the mass. Different types of wood have different densities, so using the wrong density value can result in an incorrect mass calculation.

5. Can I use this method to find the mass of any wooden object?

Yes, this method can be used to find the mass of any wooden object as long as you know its dimensions and density. Keep in mind that the accuracy of the results may vary depending on the precision of your measurements and the density of the wood.

Similar threads

  • Introductory Physics Homework Help
Replies
9
Views
2K
  • Introductory Physics Homework Help
Replies
18
Views
2K
  • Introductory Physics Homework Help
Replies
23
Views
2K
  • Introductory Physics Homework Help
Replies
9
Views
2K
  • Introductory Physics Homework Help
Replies
6
Views
2K
  • Introductory Physics Homework Help
Replies
5
Views
2K
  • Introductory Physics Homework Help
Replies
3
Views
1K
  • Introductory Physics Homework Help
Replies
7
Views
2K
  • Introductory Physics Homework Help
Replies
10
Views
2K
  • Introductory Physics Homework Help
Replies
5
Views
2K
Back
Top