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