Gravity Binds Us

Overview

Lesson 3 of 17 in Journey to the Cosmos. Students investigate gravity as an attractive force between objects with mass, then use evidence and models to explain how gravity affects falling objects, planets and moons. The lesson builds on prior learning about forces, motion and free-body diagrams.

Learning intentions

• WALT explain gravity as a force of attraction between objects with mass.
• WALT investigate how gravity affects the motion of objects.
• WALT use force diagrams and models to explain orbital motion.
• WALT distinguish between evidence, observation and scientific explanation.

Success criteria

• I can describe gravity as an attractive force acting between masses.
• I can identify the direction of gravitational force in a force diagram.
• I can use observations from an investigation to explain falling motion.
• I can explain that gravity keeps moons and planets in orbit.

Curriculum links

• Physical Science — Motion and Forces: gravity governs the behaviour and interactions of matter.
• Physical Science — Earth Systems: using models and visual representations to explore planetary motion and astronomical phenomena.
• Physical Science — Earth Systems: interpreting scientific data to compare distances and scales in space.
• Science capabilities: gathering and interpreting evidence, using models, and communicating explanations.

Lesson structure (60 minutes)

1. 0–5 min · Hook and retrieval. Teacher opens with the hook and retrieval slides, showing an image of an astronaut, Earth and the Moon, and asks: “If gravity pulls everything down, why does the Moon not crash into Earth?” Students discuss with a partner, then share one idea and one question. Briefly revisit balanced and unbalanced forces from the previous lesson.

2. 5–15 min · Direct teaching. Teacher uses the gravity teaching slides to establish that gravity is an attractive force between objects with mass, that larger masses produce stronger gravitational attraction, and that gravitational force acts towards the centre of a body. Students annotate the gravity investigation worksheet with a definition, a labelled Earth–object force diagram and the terms mass, gravity and attraction. Clarify that weight is the force of gravity on an object, while mass is the amount of matter in it.

3. 15–30 min · Falling-object investigation. In groups of four, students use a tennis ball and a sheet of paper to compare drops from the same height. They first predict which will reach the ground first, then repeat the test with the paper flat and tightly crumpled. Teacher stresses a fair test: same release height, no throwing, several trials, and one variable changed at a time. Students record observations and trial results on the results table and investigation questions. Groups consider whether air resistance, rather than different gravitational forces, explains the flat paper’s slower fall.

4. 30–42 min · Modelling gravity and orbits. Teacher demonstrates with a ball-on-string model or a projected simulation, using the orbit modelling slides. Explain that gravity continually pulls an orbiting object towards the central body while its forward motion carries it onwards; together these motions produce a curved path. In pairs, students use the labelled force arrow cards to arrange and draw arrows showing gravity acting on a falling object, the Moon and an orbiting satellite. They add captions explaining the direction of each force.

5. 42–53 min · Apply and explain. Teacher displays three scenarios through the application discussion slides: a dropped object near Earth, the Moon orbiting Earth and a planet orbiting the Sun. Students complete the explanation section of the scenario questions, using the structure: “The object is affected by gravity because… The evidence/model shows… Therefore…” Groups compare answers and identify where gravity is the central idea. Challenge students to explain why astronauts appear weightless while still being affected by Earth’s gravity.

6. 53–60 min · Plenary and assessment. Teacher returns to the opening question using the plenary slides. Students independently complete the final reflection on the exit response: “Explain how gravity can make an object fall and also help keep the Moon in orbit.” Invite two students to share answers, then collect worksheets to identify misconceptions for the next lesson.

Resources

• the complete gravity lesson slide deck
• the gravity investigation worksheet
• Tennis balls or similar soft balls, one per group
• A4 paper, including one sheet per group for crumpling
• Metre rulers or measuring tape
• Stopwatches or timer displayed on the board
• String and a soft ball, or access to an orbit simulation
• the labelled force arrow cards
• Safety goggles if using a hard ball or elevated drop point

Assessment

• Questioning during retrieval and direct teaching checks whether students understand gravity as attraction between masses and can distinguish mass from weight.
• Observe group investigations for fair-test decisions, accurate observations and appropriate explanations involving air resistance.
• Use the final written response to assess whether students can connect gravitational force with both falling motion and orbital motion.

Differentiation

• Provide a word bank, partially completed force diagrams and sentence starters such as “Gravity acts towards…” and “The evidence suggests…” for students needing support.
• Allow students to explain orally before writing, and assign clear group roles: equipment manager, releaser, recorder and reporter.
• Use visual arrows, gestures and labelled diagrams to support EAL learners; pre-teach mass, attraction, air resistance, orbit and weight.
• Extend confident students by asking them to explain how changing the mass of a celestial body could affect gravitational pull, or why an orbiting object does not simply travel in a straight line.