Yankai Chen phys1002 logbook week4 buoyancy

1
PHYS1002 Physics (Fundamental)
Lab Session, e.g. 2FND
Date
Group number/
Data set
7FND
25/3/2021
8
Lab 4: Buoyancy
The logbook consists of three parts:
 Part A: Measuring Densities
 Part B: Buoyant Force
 Design Task
 Completion
Experiment Part A – Measuring Densities
Aim: To determine the density of an ‘iceberg’ (actually a metal sphere).
Logbook 4.1
When objects have simple geometric shapes we can often use basic mathematical formulae
to calculate their volume. However, in the real world this is not always the case. Detail a step
by step method on how you would find the density of an irregularly shaped object?
Logbook 4.2
Watch the lab video to answer this section. For reference, here are the timestamps:
 0:11 Checkpoint 1 summary
 0:42 Hydrometer
 1:16 The Titanic Fluid
In the video, you saw an “iceberg” being placed in some liquids.
What does the iceberg do in each of the liquids? Based on these observations predict a
ranking for the densities of the `Titanic fluid’, fresh water and iceberg.
This part should not take longer than 60 min.
First, balance is used to measure the mass of irregular objects. In the second step, prepare
the container with volume mark and pour enough water into the object. In the third step,
the irregular object is immersed in the second step, and the height of the object before
and after being placed in the container is checked. After calculation, the volume of the
irregular object can be found. Finally, because we know that the density of something is
mass divided by "d=m/v" volume, we get the density value of irregular objects.

2
PHYS1002 Physics (Fundamental)
When the density of an object is greater than that of a liquid and gravity is greater
than buoyancy, the object sinks. When the density of an object is equal to the density
of a liquid and gravity is equal to buoyancy, the object floats. When the liquid discharged
from the object is small, the density of the object is smaller and the density of the
liquid is higher. It can be seen from the video that when the iceberg is in the water,
the ball sinks, and in the blue liquid, the iceberg is exposed to the water without sinking
to the bottom, but reveals a small part of its volume. Therefore, it can be concluded
that the density of blue liquid is greater than that of water, and the density of iceberg
is greater than that of water but less than that of blue liquid

3
PHYS1002 Physics (Fundamental)
Logbook 4.3
Open your dataset and navigate to sheet C1 on the bottom left corner.
The mass of the “iceberg” is measured using a beam balance and is provided in cell C15
(Note a beam balance is a device for measuring mass by balancing weights at two ends). The
container used to measure the water volume displaced has an interval of 20 mL. Calculate
the volume displaced by the iceberg and the uncertainties. Fill out cells B10, D10, A15 and
B15 then copy your answers to these tables:
Initial Volume (mL)
Uncertainty (mL)
Final Volume (mL)
Uncertainty (mL)
1400
10
1900
10
Volume Displaced (mL)
Uncertainty (mL)
Mass of IceBerg (g)
Uncertainty (g)
500
10
552.2
0.05
Logbook 4.4
Figure 1 depicts the hydrometers used in the data collection.
Figure 1: Hydrometers
Explain:
• What the hydrometer measures and in what units and
• Why the hydrometer scale increases downward.
Discuss with others and make an educated guess.
Hydrometer use to measure the density of liquid. The unit is kg/m^3.
For the reason that since the density of fluid is large, the hydrometer will not sink
down; and as the density of fluid is lower, the hydrometer will sink. So, the hydrometer
scale increases downward.

4
PHYS1002 Physics (Fundamental)
Logbook 4.5
Knowing the volume and mass of the iceberg you found in Logbook 3.3, calculate the density
with the uncertainty, fill in cells B3, C2, C3, and C4 in the Excel spreadsheet, C1. (Refer to
the Uncertainties Supplement from your first lab on how to propagate uncertainties) The
intervals on the hydrometer are 5 kg/m3 apart. Copy your answer into this table:
Material
Density (kg/m3)
Uncertainty (kg/m3)
Water
1000
2.50
Iceberg
1104
22.2
Titanic fluid
1180
2.50
Does this agree with your earlier prediction when ranking the densities?
Part B – Buoyant Force
Aim: To measure the buoyant force acting on an `iceberg’, in water and `Titanic fluid’.
For reference, the video timestamp is 1:51 Checkpoint 2 summary.
Planning & Predicting:
In this experiment, you will measure the buoyant force acting on an `iceberg’, as shown in
Figure 2. Consider the case of the iceberg hanging from a spring balance as shown in the
Figure. In Figure 2a the iceberg is ready to be immersed in fresh water; in Figure 2b it is partly
immersed in the water; in Figure 2c it is fully immersed but not in contact with the bottom of
the beaker; and in Figure 2d it is resting on the bottom of the beaker.
Figure 2: An iceberg hanging from a spring balance is lowered gently into a container of water.
Yes,
This part should not take longer than 40 min.

5
PHYS1002 Physics (Fundamental)
Logbook 4.6
For each situation identify which of the following forces are acting and their direction (up or
down).
(a) weight force (W)
(b) buoyant force of the water (B)
(c) pull of the spring balance (P)
(d) contact force of the bottom of the beaker on the iceberg (C).
Copy the diagrams into your Logbook. On each diagram draw arrows (refer to the theory box
below) showing the vertical forces acting on the iceberg. Label the arrows clearly.
Insert screenshot of free body diagrams (or picture of hand-drawn free body diagrams)