To Float or Not to Float - A Lesson on Density
Intermediate, 7th Grade, 8th Grade
This lesson discusses density as a property of matter. Students will use the formula to calculate density to determine if an object/material will sink or float.
Materials and Resources
Density Activity Sheet.doc
To Sink or To Float-Finding Density.doc
Density lesson organizer.notebook
Density lesson organizer.pdf
Two 45-minute periods
Students will learn:
- To explain and define density.
- To calculate density.
- To explain how to use density to identify a substance.
- Ice Cubes
- Several blocks of wood and metal (or other materials)
- Rulers and Triple Beam Balance
- 2 Clay Balls (the clay should be the same kind and same amount)
- 2 Large Container with Water
- Graduated Cylinder and 40ml of water.
- Internet Access for additional support from Brain Pop and United Streaming. These websites requires a subscription
- SMART Board software, SMART Board, and projector
Provide students with:
- 2 graduated cylinders
- triple beam balance
- cooking oil
Present the question: What would you rather carry through a dessert, a pound of feathers or a pound of lead?
After discussing the students’ answers, point out that a pound of feathers is the same as a pound of lead. The main difference is that a pound of lead is smaller (has less volume) than a pound of feather.
Review mass (the amount of material/”stuff” an object has) and volume (the amount of space an object takes up).
Write the formula for finding density on the board.
Allow students to work together to complete the Assessment Activity - Density
- Identify the horizontal line in the formula means to divide the number on top by the number on the bottom.
- Try several examples before introducing density.
- Students can practice using the blocks of wood and metal to find density.
- After students practice, explain the concept of density (a measure of how tightly the matter of a substance is packed into a given volume).
- Density can also be used to identify particle substances because the density of a substance does not change regardless of the size or shape of the piece of substance.
- Show the class the clay boat and ball. Both objects should be made of the same kind of clay and the amount of clay.
- Invite the students to predict if the clay objects will sink or float.
- Have a large container with water to finish the demonstration.
- After they have discussed their predictions place the objects in the water. Let the students observe and discuss why the clay boat floats while the clay ball sinks.
- Finally explain that by changing the shape of the clay from a ball into a boat the volume of the clay was changed therefore changing the density.
- Students will then find the density of water and cooking oil. They will determine what the density of any object must be for a substance to float or sink when placed in water.
- There is an assessment activity – “To Sink or to Float" in Word format.
- Activity Sheet - Density
- Activity Sheet - To Sink or to Float