Forces, Motion, and Friction

Introduction

Every time you kick a ball, open a door, ride a bicycle, or slide a book across a desk, you are seeing forces and motion at work. A force is a push or a pull. Motion describes a change in an object's position over time. Friction is a force that can slow motion, stop sliding, or help objects grip each other.

In this course, you will investigate how forces change motion, how gravity pulls objects toward Earth, and how different kinds of friction affect everyday life. You will also learn how scientists make fair tests, collect measurements, and explain results using evidence.

The image shows several examples of forces. Look for arrows: in science diagrams, arrows can show the direction of a force. A longer arrow can also be used to show a stronger force.

As you watch the video, listen for examples of pushes, pulls, contact forces, and forces that can act from a distance.

Learning Goals

By the end of this aiMOOC, you should be able to:

Forces: Describe a force as a push or pull and identify its direction.
Balanced and unbalanced forces: Explain why balanced forces do not change motion and why unbalanced forces can change motion.
Motion: Describe motion using position, distance, time, direction, and speed.
Friction: Explain how friction can be useful or unwanted.
Gravity and air resistance: Compare gravity with air resistance during a fall.
Fair testing: Plan a simple investigation, control variables, measure results, and use evidence to support a conclusion.

Safety First

Use lightweight classroom objects such as toy cars, books, blocks, paper, and rubber erasers. Keep ramps low and stable. Do not run experiments on stairs, roads, or slippery floors. Never throw hard objects at people. Ask a teacher or responsible adult to supervise any activity that uses moving equipment.

Forces: Pushes and Pulls

A force is an interaction that can change an object's motion or shape. You make a contact force when you push a box or pull a drawer. Some forces can act without direct contact. Gravity pulls objects toward Earth, and magnets can attract or repel some materials.

Scientists measure force in newtons, written with the symbol N. For Grades 5–6, the most important ideas are that a force has a strength and a direction.

Imagine pushing a toy car forward. A stronger forward push can create a bigger change in its motion than a weaker push. If another force pushes equally hard in the opposite direction, the forces may balance.

Force Arrows

A force arrow begins on the object that experiences the force. The arrow points in the direction of the force. You can compare arrow lengths to show which forces are stronger.

When you read a force diagram, ask two questions: Which object is receiving the force? and Which way does the arrow point? These questions help you avoid mixing up the object causing a force with the object experiencing it.

Balanced and Unbalanced Forces

Forces are balanced when their overall effect, called the net force, is zero. Balanced forces do not change an object's motion. A book resting on a desk can have balanced forces: gravity pulls downward while the desk pushes upward.

Balanced forces do not always mean that an object is stopped. An object can also move at a constant speed in a straight line when the forces on it are balanced.

Forces are unbalanced when the net force is not zero. An unbalanced force can make an object speed up, slow down, start moving, stop moving, or change direction.

This idea is connected to Newton's first law of motion: an object's motion does not change unless an unbalanced force acts on it.

A Newton's cradle shows moving balls colliding and pushing on one another. Watch how motion can be transferred through an interaction.

Motion: Describing Change

Motion means that an object's position changes compared with a reference point. A reference point might be a tree, a wall, a start line, or another object.

To describe motion clearly, you can record:

Distance: How far the object travels.
Time: How long the motion takes.
Direction: Which way the object moves.
Speed: How quickly distance is covered.

A simple way to calculate average speed is:

average speed = distance ÷ time

For example, if a toy car travels 10 metres in 5 seconds, its average speed is 2 metres per second.

While you watch, notice the difference between speed and motion with direction. For this course, you mainly need to measure and compare speed.

Speeding Up, Slowing Down, and Turning

A change in speed or direction is called acceleration. You do not need complicated equations to recognize it. A bicycle speeding up, a rolling ball slowing down, and a car turning a corner are all changing their motion.

An unbalanced force causes a change in motion. The direction of the net force helps determine the direction of the change.

In this stroboscopic image, the gaps between later positions of the falling ball become larger. That pattern shows that the ball is moving faster as it falls.

Gravity and Air Resistance

Gravity is an attractive force between masses. Near Earth's surface, gravity pulls objects toward the ground. If you drop a ball, gravity causes its downward speed to increase.

Gravity is not the only force on many falling objects. As an object moves through air, the air can push against its motion. This force is called air resistance or drag.

The diagram shows two opposite forces on a falling object: gravity downward and air resistance upward. The sizes of the forces can change during a fall.

A wide parachute increases air resistance by meeting more air. Shape, speed, and exposed area can all affect air resistance.

Try It: Paper Drop Investigation

Take two sheets of the same paper. Leave one sheet flat and crumple the other into a loose ball. Drop them from the same height at the same time. Observe which reaches the floor first. Then explain how shape and air resistance may have affected the motion. Repeat the test several times before making a conclusion.

Friction

Friction is a contact force that resists relative motion, or the attempt to move, between surfaces that touch. Friction often acts opposite the direction in which one surface is sliding or trying to slide across another.

In the diagram, the applied force and friction point in opposite directions. If the applied force becomes large enough to overcome the friction that prevents sliding, the object can begin to move.

As you watch, compare friction before an object starts sliding with friction while it is moving.

Types of Friction for This Course

Static friction acts when two surfaces are not sliding past each other. It can stop an object from beginning to slide. This is the grip that helps your shoes stay in place on the ground.

Sliding friction acts when surfaces slide across each other. A book sliding across a desk experiences sliding friction.

Rolling resistance opposes the motion of a rolling object. Wheels can often make transport easier because rolling resistance is usually smaller than the friction involved in sliding the same load.

The image shows a wheel and the forces involved in rolling resistance. You do not need to calculate these forces; focus on the idea that rolling motion still faces resistance.

Useful and Unwanted Friction

Friction is useful when you walk, write with a pencil, grip an object, or use bicycle brakes. Without enough friction, your shoes would slip and tyres would have trouble gripping the road.

Friction can also be unwanted. It can slow moving parts, produce heat, and cause surfaces to wear. Engineers may use smoother surfaces, wheels, ball bearings, or lubricants to reduce unwanted friction.

Ice skating is a useful real-world example for thinking about friction, balance, and motion. After watching, identify where skaters need low friction and where they still need enough grip to control their movement.

What Changes Friction?

Surface material and texture matter. A rough carpet and a smooth tabletop usually affect the same toy car differently. How strongly two surfaces are pressed together can also affect friction.

Do not use the rule “rough always means more friction” for every material. Real surfaces behave in different ways. A fair test changes one factor at a time while keeping other conditions as similar as possible.

Forces Working Together

Most moving objects experience several forces at the same time. A cyclist may push on the pedals, the tyres interact with the road, gravity pulls downward, the ground supports the bicycle, and air resistance acts against the motion.

To understand what happens, identify the forces and ask whether they are balanced. Then predict how the object's motion will change.

A useful thinking routine is:

Name the object. Decide which object you are studying.
Find the forces. List the pushes and pulls acting on that object.
Show directions. Draw force arrows.
Compare the forces. Decide whether they balance.
Predict the motion. Explain whether the object will keep the same motion or change speed or direction.

Cause and Effect Examples

A soccer ball at rest begins moving when a player kicks it because the kick provides an unbalanced force.

A rolling ball slows on carpet because friction acts against its motion.

A book stays at rest on a table because the downward pull of gravity and the upward support force from the table balance.

A bicycle can turn because forces between the tyres and the road change the direction of its motion.

Investigating Forces and Friction

Scientists use evidence rather than guesses. A good classroom investigation has a clear question, one main variable that changes, measurements that can be compared, and repeated trials.

One possible question is: How does surface type affect how far a toy car rolls?

You could use the same toy car, the same ramp, and the same starting point. Change only the surface after the ramp, such as smooth card, cloth, or carpet. Measure the distance the car travels after leaving the ramp. Repeat each test and compare the results.

Planning a Fair Test

A variable is something that can change. The variable you choose to change is the independent variable. The result you measure is the dependent variable. Conditions you keep the same are control variables.

For a toy-car friction test:

Changed variable: The surface material.
Measured result: The distance the car rolls.
Kept the same: The car, ramp height, start point, and release method.

Repeat trials because one result can be unusual. A simple table of measurements can help you spot patterns.

Using Evidence

A strong conclusion answers the investigation question and uses measurements as evidence. Instead of writing “The carpet had more friction because I think so,” write a statement such as “The car travelled the shortest distance on the carpet in most trials, so the carpet produced more resistance to its motion in this test.”

Be careful not to claim more than your experiment tested. If you only tested three surfaces with one toy car, your conclusion should describe those materials and that setup.

Interactive Tasks

Quiz: Test Your Knowledge

What is a force? (A push or pull) (!A measure of temperature) (!A type of material) (!A unit of time)

What does motion describe? (A change in position over time) (!A change in colour) (!A kind of energy source) (!A measurement of mass)

Which force pulls objects toward Earth? (Gravity) (!Friction) (!Magnetism) (!Sound)

What happens to motion when all forces are balanced? (The motion does not change) (!The object must stop) (!The object must speed up) (!The object must turn)

What can an unbalanced force do? (Change speed or direction) (!Remove all mass) (!Change a solid into light) (!Make time run backward)

Which surface will often create more friction for the same sliding object? (A rough surface) (!A vacuum) (!Empty space) (!A beam of light)

Why is friction useful when you walk? (It helps your shoes grip the ground) (!It removes gravity) (!It makes your mass smaller) (!It stops all forces)

What happens to average speed when the same distance is travelled in less time? (The speed increases) (!The speed becomes zero) (!The mass increases) (!The direction disappears)

What is air resistance? (A force from air that opposes motion) (!A pull only from magnets) (!A force found only under water) (!A unit for measuring distance)

Why can wheels make a load easier to move? (Rolling resistance can be smaller than sliding friction) (!Wheels remove the mass) (!Wheels stop gravity) (!Wheels create empty space)

Memory Game

Force	A push or pull that can change motion
Motion	A change in position over time
Friction	A contact force that resists relative motion
Gravity	An attractive force that pulls objects toward Earth
Speed	Distance travelled in a certain amount of time
Net force	The overall effect of all forces on one object

Drag and Drop

Match the correct terms.	Topic
Speeds up	A scooter gains speed after a forward push
Slows down	A rolling ball loses speed on carpet
Changes direction	A bat sends a moving ball another way
Balanced forces	A book remains still on a table
Unbalanced forces	One tug of war team pulls harder and the rope moves

Match each description, then explain which forces you think are acting in each example.

Crossword Puzzle

Force	What word means a push or a pull?
Motion	What word describes a change in position over time?
Friction	What force resists sliding between touching surfaces?
Gravity	What force pulls objects toward Earth?
Speed	What word tells how quickly distance is covered?
Inertia	What word describes the tendency of motion to stay unchanged unless a net force acts?

LearningApps

Cloze Text

Open-Ended Tasks

Easy

Force Hunt: Find five examples of pushes or pulls at home or school, draw each example, and add an arrow to show the force direction.
Motion Words: Choose one moving object and write a short description using the words position, distance, time, direction, and speed.
Friction Collage: Create a paper or digital collage with four examples of useful friction and four examples of unwanted friction.
Paper Drop Video: Record a short video of a flat sheet and a crumpled sheet falling, then explain how air resistance may affect what you observe.

Standard

Toy Car Surface Test: Test how far the same toy car rolls on at least three surfaces, repeat each test, record results in a table, and write an evidence-based conclusion.
Force Diagram Gallery: Draw force diagrams for a book on a table, a kicked ball, a cyclist, and a falling paper object, using labelled arrows and short explanations.
Friction Interview: Interview a cyclist, athlete, mechanic, carpenter, or other adult about where friction helps and where it causes problems in their work or hobby.
Speed Investigation: Measure a safe moving object over a known distance, record the time for several trials, calculate average speed, and compare the trials.

Advanced

Ramp Design Challenge: Build a safe low ramp for a toy car, change one feature at a time, and use measurements to explain how force and friction affect the car's motion.
Shoe Grip Investigation: Design a safe tabletop model using small material samples to compare grip, explain your fair-test variables, and avoid testing by running on slippery floors.
Motion Storyboard: Create a six-frame storyboard showing an object starting, speeding up, moving steadily, turning, slowing down, and stopping, with force arrows in each frame.
Playground Physics Report: Visit a playground with adult supervision, observe forces on a swing, slide, seesaw, or climbing equipment, and produce a report connecting your observations to balanced forces, friction, gravity, and motion.

Learning Assessment

Explain a Mystery Motion: A toy car rolls quickly on tile but stops sooner on carpet; explain the difference using friction, net force, and evidence you would collect to test your explanation.
Compare Two Force Diagrams: Draw one diagram with balanced forces and one with unbalanced forces, then explain how the motion should differ in each case.
Design a Fair Test: Plan an investigation to find out whether surface material changes sliding distance, identifying what you change, what you measure, and what you keep the same.
Use Speed Data: Given distance and time measurements for two moving objects, calculate their average speeds and explain which object moved faster using the data.
Evaluate a Claim: A classmate says that balanced forces mean an object cannot move; decide whether the claim is correct and support your answer with an example.
Transfer to Real Life: Explain how a bicycle uses both helpful friction and forces that resist motion, then suggest one design choice that could improve grip or reduce unwanted resistance.

Evidence of Learning

Evidence type	What successful learning can look like
Knowledge	You accurately explain force, motion, speed, gravity, friction, balanced forces, unbalanced forces, and air resistance in your own words.
Skills	You draw and read simple force arrows, measure distance and time, calculate average speed, plan fair tests, organize results, and compare repeated trials.
Products	You create clear diagrams, data tables, investigation reports, presentations, images, videos, or models that show how forces affect motion.
Reasoning	You use observations and measurements to explain cause and effect instead of relying only on guesses.
Transfer	You apply the ideas to new situations such as cycling, sports, playgrounds, transport, tools, and safety.

OERs on the Topic

The following English Wikipedia article gives additional background on force in physics:

Linked Learning Areas

Forces, Motion, and Friction

These ideas connect strongly with physics, engineering, mathematics, physical education, and technology. They also support scientific reading, speaking, and writing in English because you must describe evidence, compare results, and explain cause and effect clearly.

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