Density, Buoyant Force, and Archimedes’ Principle

Density, Buoyant Force,and Archimedes’ Principle

How many pennies can your boat hold?How many pennies can your boat hold?

What makes something float or sink?What makes something float or sink?

• DENSITY!DENSITY!• Let’s review:D = m / VD = m / V

Cruise Ships – 50,000 tons!Cruise Ships  50,000 tons! 

But what’s really making the less d h fldense things float?  

• When we put a boat in waterWhen we put a boat in water, what do you observe?

Water is “displaced”

But how much water is displaced?But how much water is displaced?

• http://wwwyoutube com/watch?v=eQsmq3Hhttp://www.youtube.com/watch?v=eQsmq3Hu9HA

Archimedes’ PrincipleArchimedes  Principle

The buoyant force on a fl i b dfloating or submerged 

object is equal to the weightobject is equal to the weight of the displaced fluidof the displaced fluid.

Question:Question:• A rectangular barge 300cm long and 200cm wide floats at the edge of a fresh water lake. 

• A horse jumps into the barge, and the barge j p g gsinks 12cm.  How much does the horse weigh?

720kg• 720kg

Penny‐boat challengeTake 2!Take 2!

Challenge question…Challenge question…

• I’m sitting in a boat with a really big boulderI m sitting in a boat with a really big boulder.  If I throw the boulder overboard, the water level will:level will:

A. go upB hB. stay the sameC. go down

Which bottle + weight system will float c bott e e g t syste oatHIGHER in the water?

Dipping a finger in a glass of h ill h hwater, what will happen to the 

scale reading?scale reading?

https://mrhorn.com/moodlehttps://mrhorn.com/moodle

2011 ATP P22011‐ATP‐P2