Spring Fluids Lab (Guided)
AP Physics 2 – Fluids
Name______________________
Date__________ Period_______
All answers and data must follow the PSI Lab Report Format.
*Students should know that the density of water is 1000 𝑘𝑔/𝑚3
Objective
Find the density of an object placed in water.
Materials (per team)
● Block of known mass and unknown density
● Ruler
● 500mL of Water (Water Bottle)
● Spring
● Water
● Container
Procedure
1. First, find the spring constant if you do not already have it. Measure the length of the
spring. Then attach the block to the spring and measure its new length. Use Hooke’s law
to calculate mg.
2. Submerge the entire block in water while it is still attached to the spring. Measure the
new length of the spring.
3. Compare this length (𝑥 2) with the length of the spring with the block attached out of
water (𝑥 1 ). The Buoyant Force will be equal to the spring’s force because 𝛴𝐹 = 0
4. Once you finish your calculations, check with your teacher to find how close you were to
the actual density.
Derivations
𝐹 = 𝑘𝑥
𝐹
𝐵
=𝜌
𝑤𝑎𝑡𝑒𝑟 𝑔𝑉
𝜌 = 𝑚/𝑉
Analysis:
1. What substitutions did you have to make in order to solve for the density of the block?
Why were you allowed to make them?
© njctl.org
AP Physics 2
Fluids
2. Would changing the amount of water in the container change the buoyant force? Why or
why not?
3. Should measurements be made if the spring is also submerged into water?
4. How accurate were your results? Calculate your percent error and explain any
differences between your results and the actual results.
© njctl.org
AP Physics 2
Fluids