Magnetic Force

Magnetic Force

Middle School

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Learning Objectives

• Define magnetism and explain how its invisible field creates forces.

• Describe how magnetic poles interact to create forces of attraction and repulsion.

• Model how changing the arrangement of magnets alters stored potential energy.

• Explain how Earth’s magnetic field protects the planet and creates auroras.

Key Vocabulary

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Magnetism

Magnetism is a fundamental force of nature that causes attraction or repulsion between certain materials.

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Magnetic Force

A magnetic force is the push or pull exerted between magnets or other magnetic objects.

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Magnetic Pole

A magnetic pole is a specific point at the end of a magnet where the magnetic force is strongest.

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Field

A field is an invisible region surrounding an object where a force can be felt at a distance.

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Interaction

Interaction is the mutual action between two or more objects, such as attraction or repulsion forces.

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Potential Energy

Potential energy is the stored energy an object has due to its position or arrangement.

Key Vocabulary

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System (in Physics)

In physics, a system is a collection of objects that interact with each other, like two magnets.

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Permanent Magnet

A permanent magnet is an object that stays magnetic on its own for a very long time.

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Temporary Magnet

A temporary magnet is a material that becomes magnetic only when it is in a strong magnetic field.

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Solar Wind

Solar wind is a continuous stream of charged particles that are released from the Sun's upper atmosphere.

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Compass

A compass is a tool with a magnetized needle that always aligns with the Earth’s magnetic field.

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What is Magnetism?

• Magnetism is the force of attraction or repulsion between magnets and some materials.

• A magnet always attracts objects that contain iron, like paperclips or nails.

• Permanent magnets are objects that can retain their magnetic properties over time.

• Temporary magnets, like electromagnets, are only magnetic when an electric current flows.

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Multiple Choice

Which statement best defines magnetism?

• The force of attraction or repulsion between certain materials

• The flow of electric current through a wire

• The energy an object has due to its motion

• The force that pulls objects towards the Earth

Multiple Choice

What is the primary difference between a permanent magnet and a temporary magnet?

• A permanent magnet can be turned on and off, while a temporary magnet is always on.

• A permanent magnet attracts all metals, while a temporary magnet only attracts iron.

• A permanent magnet retains its magnetism, while a temporary magnet requires an electric current to be magnetic.

• A permanent magnet is created by electricity, while a temporary magnet occurs naturally.

Multiple Choice

An electromagnet is being used to hold a pile of iron paperclips. Based on the principles of magnetism, what would most likely happen if the electric current were turned off?

• The electromagnet would become a permanent magnet and hold the paperclips.

• The electromagnet would lose its magnetism and release the paperclips.

• The electromagnet would reverse its polarity and repel the paperclips.

• The electromagnet's magnetic force would increase and crush the paperclips.

Magnetic Poles and Forces

• Opposite poles, like north and south, attract each other.

• Like poles, such as two north poles, repel each other.

• A magnet always attracts magnetic objects like paper clips.

Multiple Choice

What happens when two like magnetic poles, such as two north poles, are brought near each other?

• They repel each other.

• They attract each other.

• They cancel each other out.

• They create a magnetic field.

Multiple Choice

Which statement best describes the relationship between opposite magnetic poles?

• The north pole of one magnet attracts the south pole of another.

• The north pole of one magnet repels the south pole of another.

• The poles have no effect on each other.

• The poles will only attract metal objects, not each other.

Multiple Choice

If you bring a magnet's north pole near an object and it attracts, and then you bring the magnet's south pole near the same object and it also attracts, what can you conclude about the object?

• The object is made of a magnetic material, but is not a magnet.

• The object is also a magnet.

• The object is made of a non-magnetic material.

• The object has a strong north pole.

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Magnetic Fields: Force at a Distance

• Magnetic forces act from a distance due to an invisible magnetic field.

• This field is an area of influence extending through space around a magnet.

• We map a magnetic field using lines to show its direction and strength.

• Field lines spread from the north pole and curve around to the south pole.

Multiple Choice

What is a magnetic field?

• An invisible area of influence surrounding a magnet where a magnetic force can be felt.

• The part of a magnet where the magnetic force is visible to the naked eye.

• A force that requires two magnets to be in direct physical contact.

• The electrical charge that is stored within a magnet.

Multiple Choice

What is the function of drawing magnetic field lines?

• To show the magnetic field's direction and strength.

• To count the number of magnets in an area.

• To measure the temperature of the magnet.

• To make the invisible magnetic field visible.

Multiple Choice

Which of the following correctly describes magnetic field lines?

• They start at the south pole and curve to the north pole, with closer lines showing weaker fields.

• They start at the north pole and curve to the south pole, with closer lines showing stronger fields.

• They form straight lines between the poles, with spacing unrelated to field strength.

• They start at the north pole and curve to the south pole, with closer lines showing weaker fields.

Investigating Magnetic Fields

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Interaction at a Distance

• A compass needle moves when a magnet is brought near to it.

• The magnet and the compass do not need to physically touch each other.

• This shows the magnet's field interacting with the compass needle from a distance.

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Effect of Distance

• A magnet can attract a paperclip without touching it from a short distance.

• The attractive magnetic force is strongest when the magnet is positioned very close.

• This force gets much weaker as the magnet is moved farther away.

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Effect of Orientation

• Two magnets can either push (repel) or pull (attract) each other.

• Flipping one magnet's orientation can change the direction of the magnetic force.

• This can switch the force from attraction to repulsion, or vice versa.

Multiple Choice

What is the key characteristic of a magnet's field as described by its interaction with other objects?

• It allows the magnet to exert a force on another object from a distance.

• It requires the magnet to be physically touching an object to have an effect.

• It changes the magnet's color when another object is close.

• It makes the magnet heavier when it is near a compass.

Multiple Choice

What is the relationship between the distance from a magnet and the strength of its attractive force?

• The magnetic force becomes weaker as the distance increases.

• The magnetic force becomes stronger as the distance increases.

• The distance between objects does not affect the magnetic force.

• The magnetic force only exists when the objects are touching.

Multiple Choice

If two magnets are attracting each other, what would be the outcome if one magnet is flipped to its opposite side and also moved farther away from the other magnet?

• The magnets will now repel each other with a weaker force.

• The magnets will still attract each other but with a weaker force.

• The magnets will now repel each other with a stronger force.

• The magnets will still attract each other with the same original force.

Magnetic Potential Energy

• Energy is stored based on the arrangement of magnets in a system.

• Pushing like poles together or pulling opposite poles apart increases potential energy.

• Potential energy decreases when magnets move along with the magnetic force.

Multiple Choice

What determines the amount of magnetic potential energy stored in a system?

• The arrangement of the magnets within the system

• The speed at which the magnets are moving

• The temperature of the magnets

• The material the magnets are made of

Multiple Choice

Which of the following actions would cause an increase in a system's magnetic potential energy?

• Allowing the north pole of one magnet to touch the south pole of another.

• Pushing the north poles of two different magnets closer together.

• Letting two magnets that are repelling each other move apart.

• Sliding two magnets past each other without changing the distance between them.

Multiple Choice

Imagine two magnets are held a short distance apart with their opposite poles facing each other. If they are released and allowed to snap together, what happens to the magnetic potential energy in the system?

• It increases because the magnets are accelerating.

• It decreases because the magnets are moving with the magnetic force.

• It stays the same because energy cannot be created or destroyed.

• It becomes zero instantly as soon as they start moving.

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Earth: A Giant Magnet

• Earth acts like a huge magnet because of the molten metal in its core.

• This creates a protective magnetic field that surrounds our entire planet.

• The planet has magnetic north and south poles, where the magnetic force is strongest.

• A compass works by its needle aligning with Earth's magnetic field to point north.

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Multiple Choice

What causes Earth to act like a giant magnet?

• The molten metal in its core

• The rotation of the planet on its axis

• The gravitational pull of the moon

• The oceans covering its surface

Multiple Choice

What is the relationship between a compass and Earth's magnetic field?

• It is pulled by the planet's gravitational force.

• It aligns with the planet's magnetic field to point north.

• It detects heat coming from the North Pole.

• It is repelled by the force at the South Pole.

Multiple Choice

If Earth's core were to cool down and become solid, what would be the most likely consequence?

• The protective magnetic field would disappear.

• The magnetic force at the poles would become stronger.

• A compass needle would point south instead of north.

• The planet would stop rotating on its axis.

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Earth's Protective Shield

• The sun emits a stream of harmful charged particles called solar wind.

• Earth's magnetic field acts as a shield, protecting us from this radiation.

• It deflects these harmful particles, guiding them away toward the Earth’s poles.

• This interaction creates the spectacular light shows known as the auroras.

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Multiple Choice

What is the primary function of Earth's magnetic field?

• It causes the sun to release streams of charged particles.

• It pulls harmful radiation directly to the Earth's surface.

• It acts as a shield that protects Earth from harmful solar particles.

• It creates light shows at the equator for most of the year.

Multiple Choice

What is the direct cause of the auroras?

• The reflection of sunlight off the planet's ice caps.

• The deflection of solar wind particles by Earth's magnetic field.

• The high concentration of oxygen at the Earth's poles.

• The gravitational pull of the moon on Earth's atmosphere.

Multiple Choice

Based on the information, what would be the most likely outcome if Earth's magnetic field suddenly disappeared?

• The auroras would become much brighter and more frequent.

• The sun would stop emitting streams of charged particles.

• Earth would be exposed to a greater amount of harmful radiation.

• The particles would be concentrated at the equator instead of the poles.

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Common Misconceptions

Misconception	Correction
Forces need to touch an object to have an effect.	Magnetic forces act at a distance through invisible magnetic fields.
Magnetic fields are flat, two-dimensional lines.	Magnetic fields are three-dimensional, extending in all directions around a magnet.
The geographic North Pole is also a magnetic north pole.	Earth's magnetic pole in the north is actually a magnetic south pole.
Magnets can only attract other magnets.	Magnets also attract materials like iron and steel.

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Summary

• Magnetic forces act from a distance because of an invisible magnetic field.

• Like poles repel and opposite poles attract, which helps predict their movement.

• Magnetic fields are proven by their effects on objects without any contact.

• Potential energy is stored in magnets and changes with their position.

• Earth's magnetic field is vital for navigation and protection from solar wind.

• Auroras are visible evidence of Earth's magnetic field blocking solar particles.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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