1 of 24

Buoyancy and Surface Tension

Science FUNdamentals

2 of 24

OUTLINE

  • Buoyancy
    • densities
  • Surface Tension

3 of 24

Buoyancy

4 of 24

Part 1: Buoyancy

​

  • Took a bath and noticed level of water rose when he went in and fell when he left
  • Rise in water = size of object
  • Some objects sink in water while others do not
  • Proposed buoyant force in water opposing gravity (Newton’s Universal Law)

​

What is Archimedes’ principle?

​

5 of 24

Archimedes Principle

The force on the object (Buoyant force)

is equal to the weight of displaced water

Carroll, Brad. "Archimedes' Principle." Archimedes' Principle. N.p., n.d. Web. Aug. 2020.

6 of 24

Buoyant Force

Density of fluid

Volume of object

​

things that affect buoyant force:

​

​

7 of 24

Object Sinks

buoyant force < force of gravity

Buoyant Force

Buoyant Force

Gravitational

Force

8 of 24

Experiment Time:

Coke vs. Diet Coke

VIDEO LINK

9 of 24

What happened?

  • The 2 cans of pop have different densities
  • Coke sinks, Diet Coke floats
  • Coke sinks because it has higher density (has lots of sugar in it!)

10 of 24

Experiment Time:

Floating and Sinking Egg

VIDEO LINK

11 of 24

What happened?

  • Water is not dense enough to support the weight of the egg → the egg sinks!
  • Saltwater has higher density than the egg→ the egg can float!

12 of 24

EXPERIMENT TIME:

Buoyancy Battles!!

Credit: Chemistry Experiment Vector Illustration By Vecteezy

13 of 24

WHICH DESIGN IS THE BEST?

  • Best boats have largest surface area and deep sides allowing the weight of the marbles to spread out more

14 of 24

EXPERIMENT TIME:

Fun with Density

​

VIDEO LINK

Credit: Chemistry Experiment Vector Illustration By Vecteezy

15 of 24

What Happened?

  • Alka-Seltzer tablet reacts with water and creates gas (CO2)
  • Bubbles push droplets of water

up through the oil

  • Density of water is greater than oil
  • When it reaches the top, the air bubble pops
  • Lava Lamps and Submarines!

​

16 of 24

Surface tension

02

17 of 24

  • Water particles attract each other like magnets
  • Attractive force is like glue that keeps water together
  • E.g. Water striders

Part 4: Surface Tension

18 of 24

Surface Tension = water molecule’s ability to resist breaking apart the forces that keep water molecules together

What is Surface Tension?

19 of 24

EXPERIMENT TIME:

Pepper and Soap/Paper Boat

​

VIDEO LINK

Credit: Chemistry Experiment Vector Illustration By Vecteezy

20 of 24

What Happened?

  • Pepper is light so it floats on water (surface tension of water)
  • Soap breaks the surface tension!
  • Pepper no longer floats on top

and shoots to the side

  • The same thing happens with the boat except the boat will not sink because it is too large

​

Pepper and Water Science Trick. Youtube, uploaded by DaveHax, 20 March 2015. https://www.youtube.com/watch?v=ho0o7H6dXSU

21 of 24

EXPERIMENT TIME:

Coin Eye Dropper

​

Credit: Chemistry Experiment Vector Illustration By Vecteezy

22 of 24

EXPERIMENT TIME:

​

​

Credit: Chemistry Experiment Vector Illustration By Vecteezy

23 of 24

  • Bubbles is carbon dioxide
  • Surface tension prevents these bubbles from expanding
  • Mentos contain oils and emulsifiers which overcome this surface tension causing coke to foam!

Surface Tension

24 of 24

QUESTIONS?

24