Experiment 1: Fluid Statics

Purpose:

The purpose of this experiment is to anaylyze the fluid statics.

Equipment used:

(this picture I get from other group because we forget to take the picture)



force probe, String, Overflow can, Beaker to catch overflow, Metal cylinders with hooks or tie with string, Meter stick, Vernier caliper or micrometer caliper.




Part I Underwater Weighing Method:

use Force Probe and computer to determine the weights of a metal cylinder in air is: 0.058N


use Force Probe and computer to determine the weights of same meta cylinder when it completely submerged in water: 0.040N


from the free body diagram we can get the equation:


Buoyant force = weight of metal cylinder - tension force


Buoyant force = 0.058N- 0.040N = 0.018N

Part II Displaced Fluid Method:

measure the mass of a dry beaker : 0.10kg

Obtain an overflow can and fill it with water. excess water will drip from the overflow spout for a few secneds untial it stops dripping. place the overflow can near the edge of the table so that the spout extends over the edge, then hold the dry beaker under the overflow spout, then carefully submerged the metal cylinder into the overflow can, catching the overlfow water in the beaker. then measure the mass of the beaker with spout water.

Beaker with spout water: 0.020kg

mass of water = Beaker with spout water - Beaker = 0.020 - 0.010 = 0.010kg

According to Archimede's principle, this value will be equal to the buoyant force = 0.010kg * 9.8 = 0.098N

Part III Volume of Object Method:

First we need to find the volume of the metal cylinder:

V = pai* (d/2)^2*h

we use vernier caliper and micrometer caliper to get the height of the metal cylinder is 0.05 meter, and the diameter of the metal cylinder is 0.016 meter.

V = 3.14*(0.016/2)^2*0.05 = 0.00001 m^3

The expression for the weight of the displaced water in terms of the volume of the cylinder and the density of the fluid (water):

buoyant force = density of the water * volume of the metal cylinder

buoyant force = 1000*0.00001 = 0.01N

Summary:

this experiment, we use three ways to calculate the buoyant force when the metal cylinder completely submerged in water, in first way, we get the buoyant force is 0.018N, second way, we get the buoyant force is 0.098N, third way, we get the buoyant force is 0.01N. the first and second methods are experimental value, the third way is theoretical value. the three buoyant force are different because different method have their own error percent, and different method has different error percent.

In the first method, when we use force probe which connect to computer to measure the weight of the metal cylinder, it is hard to set the initial value of the force probe to be zero, and during the experiment, there could have some extral force exert on the force probe, and the weight of the metal cylinder itself is light, so the error percent compare to theoretical value is big.

In the second method, we calculate the weight of the water which are overflow from the beaker which is full filled with water to estimate the magnitude of the buoyant force. I think this method error percent is largest, during the experiment, when we lower the metal cylinder into the overflow beaker we can not control the overflow water flow to another beaker, so the actual volume of water we get is larger than the valume of metal cylinder. so it is a very big error percent

I think the third was the most accurate, because we measure the diameter and height of the metal cylinder to get its volume, and then multiply by the density of the water, the only error percent we can make is when we measer the diameter and the height of he metal cylinder, but the error percent is very small, so compare to other two methods, the third method is the most accurate.

In the first method, if the metal cylinder touching the bottom of water container, the buoyant force will be higher then currect value. because if the cylinder touch the bottom, there is another force support the cylinder up which have the same direction of the buoyant force, so in the calculation, we will roughly calculate the buoyant force include the supprot force, so the value of the buoyant force will be larger then normal value.