Science · Year 7 · Forces in Action · Summer Term

Effects of Forces on Motion and Shape

Investigating how forces can change an object's speed, direction, or shape.

• National Curriculum Attainment Targets
• KS3: Science - Forces

About This Topic

Gravity and space explore the forces that shape our solar system and the universe. Students learn about the gravitational pull of the Sun and planets, and how this pull keeps celestial bodies in orbit. They also investigate the difference between mass and weight and the causes of the changing phases of the moon.

This topic aligns with the National Curriculum attainment targets for space physics and forces. It provides a grand perspective on our place in the universe and the fundamental laws that govern it. Understanding gravity and space is essential for students to appreciate the scale and complexity of the cosmos. This topic particularly benefits from hands-on, student-centered approaches where students can physically model the patterns of planetary motion.

Key Questions

1. Explain how forces can change the motion of an object.
2. Analyze how forces can deform an object's shape.
3. Predict the outcome of applying different forces to a stationary object.

Learning Objectives

• Explain how applying a resultant force causes an object to accelerate, change speed, or change direction.
• Analyze how forces can cause an object to deform, distinguishing between elastic and inelastic changes.
• Predict the effect of applying balanced and unbalanced forces on a stationary object's motion.
• Calculate the resultant force acting on an object when multiple forces are applied in the same or opposite directions.

Before You Start

Introduction to Forces

Why: Students need a basic understanding of what a force is (a push or pull) before investigating its effects on motion and shape.

Properties of Matter

Why: Understanding that objects have mass and occupy space is foundational to comprehending how forces affect them.

Key Vocabulary

Force	A push or a pull on an object that can cause it to change its motion or shape.
Resultant Force	The overall force acting on an object when all individual forces are combined. It determines the object's acceleration.
Balanced Forces	When two or more forces acting on an object are equal in magnitude and opposite in direction, resulting in no change in motion.
Unbalanced Forces	When forces acting on an object are not equal and opposite, causing a change in the object's motion (acceleration).
Deformation	A change in the shape or size of an object due to the application of force.

Watch Out for These Misconceptions

Common Misconception

There is no gravity in space.

What to Teach Instead

Explain that gravity is everywhere in space and is what keeps planets in orbit. The 'weightlessness' felt by astronauts is actually due to them being in constant free-fall. Using a simulation of orbital motion can help clarify this.

Common Misconception

The phases of the moon are caused by the Earth's shadow.

What to Teach Instead

Clarify that the phases are caused by our changing view of the moon's sunlit half. A hands-on activity with a lamp and a ball (representing the Sun and Moon) is the best way to correct this common error.

Active Learning Ideas

Simulation Game: The Human Solar System

Students take on the roles of the Sun, planets, and moons. They must move in their respective orbits at relative speeds, demonstrating how gravity keeps the system together and how the moon's phases occur.

30 min·Whole Class

Inquiry Circle: Weight on Other Worlds

Groups use a set of 'planetary scales' (or calculated data) to determine their weight on different planets. They must explain why their mass remains the same while their weight changes based on the planet's gravity.

40 min·Small Groups

Think-Pair-Share: The Moon's Changing Face

Students are shown a diagram of the Earth-Moon-Sun system. They work in pairs to explain why we see different amounts of the moon's lit side from Earth, then share their explanations with the class.

20 min·Pairs

Real-World Connections

• Engineers designing car safety features, like crumple zones, use their understanding of forces to analyze how materials deform under impact, protecting occupants.
• Sports scientists analyze the forces applied by athletes during activities like throwing a javelin or kicking a football to improve technique and performance.
• Construction workers use principles of balanced and unbalanced forces when erecting bridges and buildings, ensuring structural integrity against wind and weight loads.

Assessment Ideas

Quick Check

Present students with diagrams of objects experiencing various forces (e.g., a book on a table, a tug-of-war). Ask them to identify if the forces are balanced or unbalanced and to write one sentence predicting the object's motion.

Discussion Prompt

Pose the question: 'Imagine you are pushing a heavy box across a rough floor. What forces are acting on the box? What would happen if you suddenly stopped pushing? Explain using the terms 'balanced' and 'unbalanced' forces.'

Exit Ticket

Give students a scenario: 'A spring is stretched by a weight.' Ask them to draw a simple diagram showing the forces involved and to describe whether the force is changing the object's motion or its shape, or both.

Frequently Asked Questions

What is the difference between mass and weight?

Mass is the amount of matter in an object and is measured in kilograms (kg). Weight is the force of gravity acting on that mass and is measured in Newtons (N). While mass stays the same everywhere, weight changes depending on the strength of gravity.

How can active learning help students understand gravity?

Active learning, such as creating a 'Human Solar System' or using data to calculate weight on other planets, makes the vast scales of space more relatable. By physically acting out orbits or comparing their own 'weight' across the solar system, students develop a more intuitive understanding of how gravity functions as a universal force.

What keeps the planets in orbit around the Sun?

The Sun's massive gravitational pull acts as a centripetal force, constantly pulling the planets towards it. This pull, combined with the planets' forward motion, results in a curved path or orbit.

Why do we only ever see one side of the moon?

The moon rotates on its axis at the same rate that it orbits the Earth. This is called synchronous rotation, and it means that the same side of the moon is always facing our planet.