This document provides information about buoyancy and floating objects. It includes examples of calculating volume, density, and whether objects will float based on these properties. The key points are: 1) An object's volume is calculated to determine density and if it will displace enough water to float. 2) Density is the ratio of an object's mass to its volume. If the object's density is less than the density of water (1 g/mL), it will float. 3) According to Archimedes' principle, an object floats if the buoyant force pushing up equals the gravitational force pulling down. The buoyant force depends on the amount of water the object displaces. 4) Examples

1. Starter 10/9-10:
1. What is the volume of a 3cm by
4cm by 2cm object? 24cm3
2. If the mass of #2 is 240g, what is
the density of that object? 3
240g/24cm = 10g/cm
3
3. Would it float in water? no
4. An object weighs 5N and
displaces 8N of water. Will it float?
Yes object will displace how
5. A 50mL
much water?
50mL

2. What do we know?
Balanced forces cause no change
in motion
Gravity pulls items down
Buoyant Force pushes items up
Density is a ratio of mass to
volume
Test is next week

4. Will they float?
Coke VS Diet Coke
What do we know about
them?
Mass: 390.4g & 374.1g
Volume: 380 mL

5. Which floats?
What do we need to calculate?
Yes-it is your destiny…

6. In What though?
Water
– Density = ?
Salt Water
– Density = ?

7. What is known?
What is true of both densities?
– Salt water is denser…1.1g/mL
– Water is less dense…1.0g/mL

8. Snorkeling
Easier
to snorkel in the ocean?
Mono Lake is a favorite
swimming lake - why?

9. No it’s Buoyancy
Buoy = float (latin for)
Archimedes discovered this
with the golden crown
– The crown (and our solids)
displaced an amount of water

10. Buoyancy
Buoyancy-the “floating force”
Water is “heavier” then item...
floats
Low density-more likely to
float

11. Buoyancy
Displace = push water away
– Water moves up
Archimedes Principle:
“a floating object displaces
water, the water displaced
weighs the same as the objects
weight.”

12. Boyz?
How did we calculate the
volume of irregular objects?
Remember Archimedes?
– Gold crown
Water is displaced by the
object

13. Buoyancy
Forces work on floating objects
Gravity
Gravity pulls it down
Displaced water
pushes BACK on Buoyant Force
object – buoyant force

14. Units for Buoyancy?
Forces measured in Newtons
(N)
1N = 100g pushed down on
Earth
100g

15. Buoyancy
IfGravity = Buoyant force
then object floats
What if the buoyant
force is less?

16. Uses
Hotair balloons: heat to go up
Submarines:
– fill tanks with air to surface
– fill with water to submerge

17. Practice Time!!!
Asmall boat has a mass of
76g and displaced 80 mL of
water. Does it sink or float?

18. Practice Time!!!
A small boat has a mass of
76g and displaced 80 mL of
water. Does it sink or float?
FLOAT 76g ↓
80mL↑ (bigger)

19. ↓↓↓↓↓↓↓
↑↑↑↑↑↑↑↑
So it floats – more force
going up then down

21. Practice Time!!!
A little 27 g fish displaced 25
mL of water. Does the fish
sink or float?

22. Practice Time!!!
A little 27 g fish displaced 25
mL of water. Does the fish
sink or float?
SINK 27g↓ (bigger)
25mL↑

23. Their apparent weight?
Ifthey don’t float – they do
appear to weigh something
Apparent weight = appears to
weigh a different amount
WTair= WTwater + BF

24. Their apparent weight?
 If they don’t float – they do appear
to weigh something
WTair= WTwater + BF
WTair: weight, mass
WTwater: apparent weight, weight under/in
water
BF: buoyant force, water displaced,
volume

25. WTair = WTwater + BF
Weight buoyant force
Mass water displaced
Weight-land Apparent weight volume
Weight in water
Weight under water

26. Practice Time!
A person appears to weigh
50g in water. When outside
of water they weigh 500g.
What is the buoyant force
acting on them?
WTair=WTwater+ BF
500g = 50g + ? BF=450g

27. Practice Time!
A person appears to weigh
200g in water. When outside
of water they weigh 500g.
What is the buoyant force
acting on them?
WTair=WTwater+ BF
500g = 200g + ? BF=300g

28. Practice Time!
A dog jumps into the water.
The water holds him up
because he only weighs 5g.
On land, he weighs 50g. Why
did this change?
Buoyant Force held him 45g

29. Practice Time!
A person weighs 700g but in
water, they weigh only 200g.
How many mL of water are
supporting them?
700g = 200g + ? BF=500mL

30. Observation Time!

33. Bill’s got
a boat!