Structures of Life

Electromagnetic Force

Middle School

​

Learning Objectives

• Describe how forces act on objects, either by direct contact or through a force field.

• Explain Newton's Laws of Motion and how net force affects an object's motion.

• Identify factors that affect the strength of electric and magnetic forces.

• Explain how energy is converted in motors and generators and compare different energy sources.

Key Vocabulary

​

Force

A force is simply a push or a pull that acts upon an object, causing it to move.

​

Friction

Friction is the force that resists motion when two surfaces rub against each other, creating resistance.

​

Gravity

Gravity is the natural force of attraction that exists between any two objects with mass or energy.

​

Magnetism

Magnetism is the force exerted by magnets when they attract or repel each other due to currents.

​

Field

A field is a region or area in space where a non-contact force can be felt.

​

Net Force

The net force is the overall force acting on an object, which is the sum of all forces.

Key Vocabulary

​

Newton's Laws

Three rules that explain how forces cause objects to start, stop, and change motion.

​

Circuit

A complete loop that lets electric current flow continuously from the power source and back.

​

Electromagnet

A temporary magnet made by winding wire around iron and running electric current through it.

​

Generator

A machine that uses motion and magnets to create electrical energy for homes and devices.

​

Turbine

Rotating blades that spin when pushed by water, wind, or steam, turning motion into useful work.

​

Sustainable Energy

Power produced from sources like sunlight, wind, or moving water that naturally renew and never run out.

Force, Gravity, and Friction

​

Force

• A force is simply a push or a pull on an object.

• It can make an object start moving, stop, or change its direction.

• The standard unit used to measure force is called the Newton (N).

​

Gravity

• Gravity is the invisible pulling force between any two objects with mass.

• The more massive an object is, the stronger its gravitational pull becomes.

• Earth's gravity is why an apple falls from a tree to the ground.

​

Friction

• Friction is a force that occurs when two surfaces are in direct contact.

• This force always works to resist or oppose the motion between surfaces.

• It's why a hockey puck sliding on ice will eventually slow down.

Multiple Choice

Which of the following best defines a force?

• A push or a pull on an object.

• The resistance between two surfaces in contact.

• The invisible force that pulls objects with mass together.

• The standard unit used to measure weight.

Multiple Choice

What is the primary difference between the forces of gravity and friction?

• Friction resists motion between surfaces, while gravity pulls objects toward each other.

• Friction only happens to moving objects, while gravity only affects stationary objects.

• Gravity is a type of push, while friction is a type of pull.

• Gravity requires direct contact, while friction can act over a distance.

Multiple Choice

If a hockey puck is sliding across a flat sheet of ice, how do the forces of gravity and friction affect it?

• Gravity would pull the puck down onto the ice, and friction would cause it to slow down.

• Friction would pull the puck down onto the ice, and gravity would cause it to slow down.

• Gravity would be the only force acting on the moving puck.

• Friction would make the puck move faster across the ice.

Types of Force Fields

​

Gravitational Fields

• ​Gravitational fields exist around any object that possesses mass.

• ​​These fields are always attractive, pulling other objects in.

• ​This is why a ball will fall to the Earth.

​

Magnetic Fields

• ​Magnetic fields are found around magnets and moving electric charges.

• ​​They attract or repel other magnets and certain metals.

• ​The field's strength decreases as the distance increases.

​

Electric Fields

• ​Electric fields are created by and exist around electric charges.

• ​​These fields can exert forces on other electric charges.

• ​Their strength weakens with distance from the charge.

Multiple Choice

What property must an object have to create a gravitational field?

• An electric charge

• A north and south pole

• Mass

• Movement

Multiple Choice

What is a key difference between the forces exerted by gravitational fields and magnetic fields?

• Gravitational fields are created by charges, while magnetic fields are created by mass.

• Gravitational fields only attract, while magnetic fields can attract or repel.

• Gravitational fields get stronger with distance, while magnetic fields get weaker.

• Gravitational fields affect all objects, while magnetic fields only affect other magnets.

Multiple Choice

A scientist measures the force from a magnet and from an electric charge. What is a critical principle they must account for that applies to both fields?

• The strength of both fields weakens with increased distance.

• Both fields are created by and exert forces on electric charges.

• Both fields are only capable of attracting other objects.

• The strength of both fields increases with increased mass.

​

​

Net Force and Newton's First Law

Balanced Forces

• Forces that are equal in size and opposite in direction are known as balanced forces.

• Balanced forces cancel each other out, resulting in a net force of zero.

• When forces are balanced, there is no change in the object's current state of motion.

Unbalanced Forces

• Unbalanced forces are not equal and opposite, so they do not cancel each other out.

• They cause a change in an object's motion, like its speed or direction.

• This principle is explained by Newton's First Law, also known as the law of inertia.

Multiple Choice

According to Newton's First Law, what must be true for an object to change its speed or direction?

• The forces acting on the object are balanced.

• The forces acting on the object are unbalanced.

• The object has no forces acting on it.

• The object's inertia is increasing.

Multiple Choice

What is the relationship between balanced forces and an object's motion?

• The object begins to speed up.

• The object changes its direction.

• There is no change in the object's motion.

• The object immediately stops moving.

Multiple Choice

A student pushes a box across the floor at a constant speed. Suddenly, the box starts to slow down and stops. What can you conclude about the forces acting on the box when it started to slow down?

• The forces acting on it became balanced.

• The forces acting on it became unbalanced.

• The net force on the box became zero.

• The box's inertia disappeared.

​

​

Newton's Second and Third Laws

Second Law of Motion

Third Law of Motion

• ​This law states that for every action, there is an equal and opposite reaction.

• ​​When you push on an object like a wall, it also pushes back on you.

• ​The force exerted by the wall is equal in strength to the force you apply.

Multiple Choice

What does Newton's Second Law of Motion explain?

• How force, mass, and acceleration are related to one another.

• That for every action, there is an equal and opposite reaction.

• Why objects in motion tend to stay in motion.

• How gravity affects objects with different masses.

Multiple Choice

Based on Newton's Third Law of Motion, what happens when you push on a wall?

• The wall pushes back on you with a force of equal strength.

• The wall pushes back on you with a weaker force.

• The wall does not exert any force on you.

• Your force is transferred into the ground.

Multiple Choice

If you apply the same amount of force to a heavy box and a light box, what prediction can be made using Newton's Second Law?

• The lighter box will accelerate more quickly.

• The heavier box will accelerate more quickly.

• Both boxes will accelerate at the same rate.

• Neither of the boxes will accelerate.

​

​

What is Magnetism?

• Magnetism is a non-contact force that is created by magnets.

• Every magnet creates a magnetic field that weakens with distance.

• Like poles repel each other, while opposite poles will attract.

• Permanent magnets can induce temporary magnetism in some metal objects.

​

Multiple Choice

Which statement best describes magnetism?

• A non-contact force created by magnets.

• A contact force that requires touching.

• A type of energy created by electricity.

• A force that only works on plastic objects.

Multiple Choice

What is the cause-and-effect relationship that explains why two magnets would push each other away?

• Placing two like poles near each other.

• Placing opposite poles near each other.

• The magnets losing their magnetic field.

• The magnets getting weaker with distance.

Multiple Choice

If a permanent magnet is used to induce temporary magnetism in a paperclip, what can be predicted about the paperclip's magnetic field?

• Its magnetic field will be strongest up close and too weak to attract objects from far away.

• It will become a permanent magnet with a field that never weakens.

• Its magnetic field will get stronger as you move farther away from it.

• It will now repel all other metal objects instead of attracting them.

​

​

What Is an Electric Circuit?

• An electric circuit is a complete path for electric current to flow.

• It needs a source (battery), a path (wires), and a load (bulb).

• Conductors let electricity pass, while insulators block it.

• Current is determined by the source’s voltage and the load’s resistance.

​

Multiple Choice

What is an electric circuit?

• A complete path for electric current to flow.

• A source of stored electrical energy.

• A material that blocks the flow of electricity.

• A device that measures electric current.

Multiple Choice

Which statement best describes the role of conductors and insulators in a circuit?

• Conductors form the path for electricity, while insulators are used to block it.

• Insulators create the electric current, while conductors are the load.

• Conductors provide the power, while insulators complete the path.

• Insulators store energy, while conductors use the energy.

Multiple Choice

What would most likely happen if the wire connecting a battery and a bulb was replaced with a piece of plastic?

• The current would stop flowing because the plastic breaks the complete path.

• The bulb would get brighter because plastic is a type of conductor.

• The voltage from the battery would increase to push through the plastic.

• The resistance of the bulb would decrease to pull more current.

​

​

Electromagnetism

• Electric current in a wire creates circular magnetic field lines around the wire.

• Wrapping a wire coil around an iron nail makes a temporary electromagnet when powered.

• Electromagnet strength grows if you increase current, add more coils, or choose better core.

• Because current can be switched, an electromagnet can be turned on or off easily.

​

Multiple Choice

What is created around a wire when an electric current flows through it?

• A magnetic field

• A source of light

• A chemical reaction

• A buildup of static electricity

Multiple Choice

What is the key advantage of an electromagnet made by wrapping a wire around an iron nail?

• It can be turned on and off.

• It is always a permanent magnet.

• It works without any power.

• It is made from a special type of metal.

Multiple Choice

A student builds a simple electromagnet but finds it is too weak to pick up a paperclip. Based on the principles of electromagnetism, what is the most effective way to increase its strength?

• Increase the number of wire coils around the nail.

• Use a plastic core instead of an iron nail.

• Decrease the electric current flowing through the wire.

• Unwrap some of the wire coils from the nail.

​

​

Motors and Generators

Electric Motors

• Electric motors convert electrical energy into the mechanical motion of a spinning shaft.

• A power source creates an electromagnet that interacts with permanent magnets inside the motor.

• This magnetic interaction is what causes the central part of the motor to rotate.

Electric Generators

• Electric generators do the opposite, turning mechanical motion into electrical energy.

• When a wire coil is rotated within a magnetic field, an electric current is generated.

• An external force, like wind or water, must provide the energy to turn the coil.

Multiple Choice

What is the main difference between an electric motor and an electric generator?

• A motor uses electrical energy to create motion, while a generator uses motion to create electrical energy.

• A motor uses magnetism to create heat, while a generator uses motion to create magnetism.

• A motor uses motion to create magnetism, while a generator uses electricity to create motion.

• A motor uses electrical energy to create light, while a generator uses heat to create electricity.

Multiple Choice

How does an electric motor cause its central part to rotate?

• An external force like wind or water spins a permanent magnet.

• An electromagnet powered by electricity interacts with permanent magnets.

• A wire coil is heated by an external power source.

• Mechanical motion is used to cool down a spinning shaft.

Multiple Choice

A generator turns motion into electricity by spinning a wire coil in a magnetic field. What would most likely happen if you used your hand to rapidly turn the shaft of an electric motor?

• It would generate a small amount of electrical energy.

• The motor's shaft would start spinning faster on its own.

• The permanent magnets would lose their magnetic force.

• Nothing would happen because motors cannot create energy.

​

​

Electric Cars: An Engineering Challenge

Criteria

• Electric cars use a battery to power an electric motor.

• Criteria are the requirements and goals for the car's success.

• Key criteria include performance, like acceleration, and the car's range.

Constraints

• Constraints are the limitations and challenges in the engineering design process.

• These include the battery’s energy capacity, total weight, and overall cost.

• Regenerative braking helps overcome constraints by recharging the battery during deceleration.

Multiple Choice

In the engineering design process for an electric car, what are 'criteria'?

• The requirements and goals that define a successful design.

• The limitations and challenges that restrict the design.

• The process of recharging the battery during deceleration.

• The total weight and cost of the car's components.

Multiple Choice

What is the relationship between regenerative braking and the constraints of an electric car?

• It addresses the constraint of limited battery capacity by partially recharging the battery.

• It improves the car's performance by making the motor more powerful.

• It reduces the car's total weight by using lighter materials.

• It helps meet the goal of high acceleration by cooling the engine.

Multiple Choice

An engineer wants to design an electric car with the longest possible range. Based on the typical trade-offs in car design, what is the most likely challenge they will face?

• Increasing the battery's size to improve range would likely also increase the car's total weight and cost.

• Improving the car's acceleration will automatically decrease the car's total weight.

• Decreasing the battery's energy capacity is the best way to increase the car's range.

• Reducing the car's cost is the only way to improve its performance and acceleration.

​

​

Energy Generation and the Environment

Fossil Fuels

• Most electricity is generated by burning nonrenewable fossil fuels like coal and natural gas.

• The fuel heats water, creating steam that spins a turbine connected to a generator.

• This process releases greenhouse gases, which are harmful to the environment.

Sustainable Energy

• Hydropower uses the force of falling water to turn turbines and generate electricity.

• Wind power uses large turbines to capture energy from the wind to generate electricity.

• Solar power uses special cells to convert sunlight directly into electricity without turbines.

Multiple Choice

What is the primary environmental problem caused by generating electricity from fossil fuels like coal and natural gas?

• They are difficult to find underground.

• They release harmful greenhouse gases.

• They create too much steam.

• They are a renewable resource.

Multiple Choice

How are the processes of generating electricity from hydropower and wind power similar?

• They both convert sunlight directly into electricity.

• They both use a force from nature to spin a turbine.

• They both require the heating of water to function.

• They both release greenhouse gases into the atmosphere.

Multiple Choice

A company wants to build a new power plant that can generate electricity without using a turbine. Which energy source is the best choice and why?

• Fossil fuels, because they are the most common source of electricity.

• Hydropower, because it uses the force of water instead of heat.

• Wind power, because its turbines are powered by a natural source.

• Solar power, because it converts sunlight directly to electricity without a turbine.

​

Common Misconceptions

Misconception	Correction
Objects at rest have no forces acting on them.	Objects at rest have balanced forces, resulting in a zero net force.
Electricity flows from a source to a device and stops.	A complete circuit is required for electricity to flow back to the source.
Action-reaction forces cancel each other out.	These forces act on different objects, so they do not cancel out.

​

Summary

Poll

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

• 1

• 2

• 3

• 4