8th Grade Science | Position, Motion, and Scientific Thinking
Essential Question: How do units and directions describe position and motion?
Have you ever looked out of a window and watched a train pass by? Maybe you were sitting in a car when another car moved beside you.
How could you tell which object was moving? How would you explain where the object was going?
Scientists use position, direction, distance, and time to describe how objects move.
They also use a strategy called C.E.R. (Claim, Evidence, and Reasoning) to explain their observations.
Today, we will learn how to use this strategy to study the position and motion of a train.
🧠 What Is C.E.R.?
C.E.R. stands for Claim, Evidence, and Reasoning.
Scientists use this strategy to make strong arguments based on facts and observations.
C = CLAIM: What do you think?
A claim is a statement that answers a scientific question.
Your claim should be clear and based on what you observe.
Example:
Question: Where is the train located?
Claim: The train is beside the station platform.
This claim describes the train’s position.
E = EVIDENCE: How do you know?
Evidence is information that supports your claim.
Scientists collect evidence by observing objects, studying photographs, taking measurements, and completing experiments.
Example:
The photograph shows the train next to the platform. The station sign is visible behind the train.
These details help support the claim about the train’s position.
R = REASONING: Why does your evidence matter?
Reasoning explains how your evidence supports your claim using scientific ideas.
Example:
We can describe an object’s position by comparing it to another object. The station platform is a reference point that helps us explain where the train is located.
Now we have a complete scientific argument!
📍 Understanding Position: Where Is It?
Position tells us where an object is located.
But there is something important to remember: We usually describe an object’s position by comparing it to something else.
The object we use for comparison is called a reference point.
Imagine a train sitting beside a station.
You might describe its position by saying:
- The train is next to the platform.
- The train is behind the station sign.
- The train is 10 meters east of the crossing.
Each statement helps explain where the train is located.
The platform, sign, and crossing can all serve as reference points.
Think About It: If you tell someone that a train is 10 meters away, do they know exactly where it is?
Not yet! They need to know 10 meters away from WHAT and in WHICH direction.
That is why reference points and directions are important.
🧭 Understanding Direction: Which Way?
Direction tells us where an object is located or which way it is moving.
Scientists use words such as north, south, east, and west. They may also use left, right, forward, and backward when the viewpoint is clear.
Imagine standing at a train station.
A train could be:
- 20 meters east of the station.
- 5 meters north of the crossing.
- Moving west toward a bridge.
Notice that these descriptions include both a number and a direction.
The number tells us how far away something is. The direction tells us which way.
Together, they give us a clearer picture of the object’s position.
🚆 Understanding Motion: Is It Moving?
Motion happens when an object’s position changes over time compared to a reference point.
Imagine watching a train through a window.
At first, the front of the train is beside a large tree.
A few seconds later, the front of the train is beside a bridge.
The train’s position has changed compared to the tree and bridge.
This is evidence that the train moved!
But what if you only had one photograph?
A photograph can show where the train is located at one moment. It may also show clues that suggest motion.
However, one photograph usually cannot prove that an object is moving.
To confirm motion, scientists need to compare the object’s position at different times or collect other evidence.
That is an important part of thinking like a scientist: knowing the difference between what you observe and what you think might be happening.
📏 Why Do Units Matter?
Scientists use units to make measurements clear.
Here are some units you may see when studying motion:
| Unit | What It Measures |
|---|---|
| Meters (m) | Distance or position |
| Kilometers (km) | Longer distances |
| Seconds (s) | Time |
| Meters per second (m/s) | Speed |
Look at these two statements:
Statement 1: The train moved 20.
Statement 2: The train moved 20 meters east in 5 seconds.
Which statement gives you more information?
The second statement!
It tells us how far the train moved, which direction it traveled, and how much time passed.
Scientists need this information to describe motion accurately.
🔍 Speed: How Fast Is It Moving?
Speed tells us how much distance an object travels in a certain amount of time.
We can calculate speed using this formula:
Speed = Distance ÷ Time
Imagine a train travels 100 meters in 20 seconds.
100 ÷ 20 = 5
The train’s average speed is 5 meters per second (5 m/s).
This means the train traveled an average of 5 meters each second.
But speed does not tell us the direction of travel.
When we describe both speed and direction, we are describing velocity.
For example:
The train is moving east at 5 meters per second.
This tells us how fast the train is moving AND which direction it is traveling.
🖼️ Our Investigation: The Train Outside the Window
In our investigation, you will study a photograph showing a train outside a window.
Your job is to look closely at the image and describe what you observe.
Ask yourself:
- Where is the train located?
- What objects can I use as reference points?
- What visual clues help me describe its position?
- Does the photograph provide evidence that the train is moving, or can I only make a prediction?
- What measurements or additional information would help me describe its motion?
Remember, scientists do not make claims without evidence.
You should only use information that you can observe or support with scientific facts.
✏️ Using C.E.R. in Our Investigation
As you study the photograph, you will organize your ideas using C.E.R.
CLAIM — What can you say about the train?
Sentence starters:
- The train is located…
- Based on the photograph, I can tell that…
- I think the train may be moving because…
EVIDENCE — What do you see that supports your claim?
Sentence starters:
- In the photograph, I notice…
- One visual clue is…
- The train’s position compared to ___ shows…
REASONING — How does science explain your evidence?
Sentence starters:
- This evidence supports my claim because…
- A reference point helps describe position by…
- Scientists describe motion by comparing…
- I would need more information to know…
Your reasoning should explain the connection between your observations and the scientific ideas we have learned.
🌟 Why Is This Important?
Understanding position and motion helps us explain how things move in the world around us.
Scientists, engineers, pilots, and drivers use these ideas every day.
We also use position and motion when following directions, reading maps, tracking storms, and planning travel.
Learning to describe what you observe is an important scientific skill.
And using C.E.R. helps you explain your thinking in a way that others can understand.
🎯 Your Science Challenge!
Before beginning the investigation, imagine that you are sitting on a train and looking out the window.
You see another train on the tracks beside you.
Suddenly, it looks like the other train is moving backward!
Think about these questions:
- How do you know which train is moving?
- Could both trains be moving?
- What reference point could help you figure it out?
Write down one claim about the trains and one observation that might help you test your claim.
Be ready to explain your thinking!
Remember: Great scientists do not just describe what they see. They use evidence and reasoning to explain what their observations mean! 🔬
Next Steps:
- Group Work: Work in groups of 2-3 to complete the Encounter the Phenomenon activity on pages 7-9 of your workbook.
- On Your Own: Complete the Investigation Activity on page 10.
- Turn It In: Put a post-it note on page 10 of your workbook. Turn your workbook in by placing it neatly in the black crate.
- When you are done: Review the What to do When You Are Finished post.
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