Feel the Force: Magnetism · Lesson 0001 · about 10 minutes · Tiếng Việt
Magnets push and pull: reading the force from the balance
By the end of this lesson you can: say what a force is, state the two-pole rule, and explain why the balance reading goes up or down in the experiment — exactly the skill that step 5 of the method asks for.
A force is a push or a pull
A force needs no complicated definition to start: a force is a push or a pull. Pushing a bicycle, pulling open a drawer — those are forces. Force is measured in newtons (N), named after the scientist Isaac Newton. An apple resting in your palm feels a weight of about 1 N.
The investigation question is about a special kind of force: the force between two magnets. Two magnets act on each other without touching — a big difference from the bicycle, which you have to touch before you can push it.
Every magnet has two poles
Hold a flat magnet and you always find two opposite faces: one is the north pole (N), the other the south pole (S). The rule is two lines long:
- Two like poles (N with N, S with S) → repel each other.
- Two unlike poles (N with S) → attract each other.
A magnet cannot have just one pole: cut one in half and you get two new magnets, each with both an N and an S. So in the experiment, every neodymium disc always carries both poles; what changes is only which face points at the other.
The force crosses empty space: the magnetic field
The magnets push and pull without touching — what carries the force across the gap? The answer: the magnetic field. Every magnet fills the space around itself with a region of influence; enter that region and another magnet feels a force. The closer you get, the stronger the field — that is the premise of the hypothesis in the assessment: smaller distance → larger magnetic force.
The experiment: the balance is a force detector
The equipment from the assessment: a lab stand clamping a micrometer (screw gauge) with the upper magnet on it; the lower magnet stuck onto a wooden block resting on an electronic top-pan balance. The steps:
- Stick the lower magnet onto the wooden block and put the block on the balance pan.
- Press TARE/ZERO → the balance shows 0.00 g. The balance now ignores the block; from here on it only senses changes.
- Clamp the micrometer so the upper magnet hangs directly above, the two faces parallel and the axis vertical.
- Turn the micrometer to bring the magnets closer in equal steps, and read the balance at each distance.
Why does the balance reading change? Look at the lower magnet — the object sitting on the pan:
- If the magnets repel: the upper magnet pushes the lower magnet down onto the pan → the pan carries an extra force → the reading goes up.
- If the magnets attract: the upper magnet pulls the lower magnet up → the pan feels lighter → the reading goes down (it can drop below 0.00 g because of the TARE).
| What happens between the magnets | Balance reading | Why |
|---|---|---|
| repelling (like poles) | up | the push presses down |
| attracting (unlike poles) | down | the pull lifts up |
Try it yourself: press and watch the balance
This simulation mirrors the assessment's equipment. Press the two mode buttons and watch three things: the upper pole changing colour, which way the force arrow points, and which way the balance reading moves. Press TARE to return to 0.00 g.
Reading the balance: +3.40 g means the pan is carrying an extra push equal to 3.40 g — the two magnets are repelling. A negative number means the magnet is being pulled up — they are attracting. Lesson 0002 will convert grams into newtons using F = mg with g = 9.8 N/kg.
Quick check
Answer without looking back — effortful recall sticks better than re-reading.
Remember
- Like poles push apart; unlike poles pull together. Cut a magnet in half and you get two smaller magnets, each with both poles.
- The magnetic field carries the force across empty space; the closer the magnets, the stronger the force.
- A tared balance is a force detector: reading up = repelling, reading down = attracting (the pull lifts the magnet).
Recommended primary source: the Magnet and Compass simulation by PhET (University of Colorado). Open the link, then: (1) watch the field lines around the magnet; (2) press Flip Polarity and see the compass swing round; (3) drag the compass away and watch the needle deflection shrink — the field weakens as the distance grows.
Integrity note: the report must be your own work. These lessons teach the skills so you can do it yourself; if you use AI tools while learning, state it in the Declaration at the end of the report template, as the assessment requires.
Glossary → · Next lesson: From balance reading to force — F = mg (coming soon)
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