Put it in water and measure how much water is displaced.
it is easiest to do with small rocks, but can be dome with anything if you can move it and have a container large enough to hold it. place water into a container with measurment markings and place the rock into it. the amount the water level rises, called displacement, is the volume of the rock.
the force that acts on rock to change its shape or volume is stress.
Porosity is the volume of open spaces in rock or soil.
What does the water represent ? How about the rock ?
Body of water has large mass and volume. Rock has got less mass and volume. But still the rock sinks in the water. The reason is very simple. Density of the rock is more than water. Mass upon volume of the rock is more than water. So rock sinks in the water. That means rock is heavier than water, if the volume of both is same. Alternately the if you take the same mass of both, rock and water, volume of the rock is lesser than that of water.
One way to do it is fill a graduated cylinder with water and record the number, next put the rock in the water and be careful not to spill any water. Record the volume of the rock and the water together. The difference in the volumes is the volume of the rock.
Drop it in water. Fill a graduated cyllinder with water to cover the sample and record the volume. Then gently lower the rock sample into the water and record how much the water rose. The difference is the volume of the rock. Drop it in water. Fill a graduated cyllinder with water to cover the sample and record the volume. Then gently lower the rock sample into the water and record how much the water rose. The difference is the volume of the rock.
Place a specific amount of water in your bottle. Record the volume. Place the rock in the bottle. Read and record the new volume of water. Subtract the first volume measurement from the measurement after you added the rock. The difference is the volume of the rock.
The weight of the rock will be lessened by the weight of the same volume of water. If the rock weighs less than that volume of water, it will float (as does pumice). Thus, if you had a rock that has a density (weight/volume) of 2 times the same volume of water, it would weigh one half of its dry weight when in water.
Fill a graduated cylinder full of water, than drop a rock inside. The amount that the water rises will determine the volume of the rock. Amount of water level increase=volume of rock.
Fill the cylinder with water to a marked point. Then place the rock in the water and measure how much the water level rises. That will give you the amount of volume displaced by the rock and so the volume of the rock.
Divide each rock's mass by its volume. The rock with the higher number is denser. To find the volume, measure the rocks in a graduated cylinder, the one that displaces more water is denser.
Fill a bowl of water that is bigger than the rock right to the top, add the rock, collect and measure the volume of how much water is spilt. Provide the rock is not porous or very soluble this will provide the volume of the rock.
place the rock in a large container that is fillec to the brim with water, making sure you know how much water you put in. Place a tray underneath (or something similar) and place the rock in. Wait until the water stops moving, then measure the amount of water on the tray. The amount of water in the tray is the volume of the rock. E.g. the water in the tray was 20ml, so the volume of the rock is 20cm3.
Fill a beaker or measuring cylinder with water and record the volume of water indicated. Put the rock in the beaker/measuring cylinder and record the new volume of water indicated. The difference between the two volumes is the volume of the rock.
One way would be to get a container into which you could put the rock completely, fill it to the brim with water (without the rock in it), then put the rock in and measure the volume of the water that flowed out.