Science Lesson Kit · Teacher Resource
Light Refraction: Why Does a Straw Look Bent in Water? — 5E Lesson Plan
Physical Science · 50 minutes
Grade 4
5E lesson flow
01
Engage
6 min
Teacher Does
Show a bent-looking straw image next to a dry straight straw.
Students Do
Explain observations without claiming the object physically bends.
Ask
- Which part looks changed? Which part is real?
Look For
Notice an apparent offset at the waterline.
02
Explain
9 min
Teacher Does
Model light traveling from straw, through water to air and eye.
Students Do
Trace a simple bending path with the boundary clearly marked.
Ask
- Where does the light change direction?
Look For
At the water–air surface.
03
Compare
8 min
Teacher Does
Present pond mirror image and underwater coin observations.
Students Do
Distinguish reflection and refraction using evidence.
Ask
- What is bouncing? What is passing into another material?
Look For
Differentiate the two behaviors.
04
Investigate
10 min
Teacher Does
Guide one-variable side-view plastic-cup test.
Students Do
Predict, observe and record dry/wet appearance; avoid changing camera angle.
Ask
- How will we keep the comparison fair?
Look For
Same cup, straw, angle and lighting.
05
Explore
9 min
Teacher Does
Run the interactive choice, sort and light-path sequence.
Students Do
Use explanatory feedback to refine their models.
Ask
- How do we know the straw was not changed?
Look For
Evidence-based model.
06
Assess
8 min
Teacher Does
Assign the independent aquarium worksheet and exit question.
Students Do
Explain a fresh case and trace a ray.
Ask
- What is one limit of a drawn ray diagram?
Look For
Ray is a model, not a visible object.
Student goal
I can observe refraction, explain a bent-looking straw with light-ray evidence, and design a fair test.
Learning objectives
- Describe observations showing that a straight object can LOOK bent in water without changing shape.
- Use a simple ray model to explain that light changes direction when crossing between air and water at an angle.
- Design a fair, safe comparison by changing one viewing condition, keeping the object straight, and using evidence to distinguish refraction from reflection.
Materials
- Transparent unbreakable cups
- Straight drinking straws or pencils
- Water and absorbent towels
- Pictures of a coin, a pond reflection and a magnifying glass
- Printed aquarium worksheet
Before class
- Use an unbroken plastic container and room-temperature water.
- Photograph a bent-looking straw from a fixed side angle.
- Prepare dry control image as well as water-filled case.
- Review difference between refraction and reflection; do not use lasers.
Safety & supervision
Review these precautions before students begin the investigation. Follow your school's safety procedures.
- Use plastic cups instead of glass.
- Never use lasers, especially near water.
- Use a shallow amount of room-temperature water; wipe spills.
- Do not drink experiment water or taste materials.
Prior knowledge
- Light allows us to see illuminated objects.
- Some materials are transparent.
- Reflected light bounces off surfaces.
Vocabulary
- refraction
- A change in the direction of light as it travels from one transparent material into another, usually when it crosses at an angle.
- transparent
- Allowing much light through so objects behind can be seen clearly.
- light ray
- A line in a scientific model showing the direction light travels.
- boundary
- The surface where two materials, such as air and water, meet.
- reflection
- Light bouncing off a surface rather than changing direction as it passes into another material.
- apparent position
- The location where an object seems to be, which may differ from where it really is.
- lens
- A transparent, usually curved object that refracts light and may focus or spread it.
Differentiation
- Provide an enlarged image of a straw crossing the waterline.
- Give a blank waterline model with dots marking the eye and straw.
- Allow verbal claim and evidence before writing.
- Extension: observe a coin appearing higher through water, without touching the coin.
Assessment
- Explain bent appearance without claiming physical change.
- Match examples to reflection or refraction.
- Draw a ray model with a single change of direction at an interface.
- Apply learning to independent aquarium worksheet.
Exit ticket
What bends during refraction: the straw, the water surface, or the light path?
Extension
Compare lens and flat-water images and explain why shape of clear boundary matters.