Lesson 6: Mass vs Weight & Gravitational Field Strength (F_g = m g)
Exploring forces, net force calculations, motion graphs, energy, and real-world NZ physics applications.
🎯 Ngā Whāinga Akoranga | Learning Intentions
The difference between mass (amount of matter in kg, constant everywhere) and weight (force of gravity in N, F_g = m g), and Earth's gravity g ≈ 9.8 N/kg (or 10 N/kg).
Calculate weight force F_g using F_g = m g on Earth, Moon, and Mars, and explain why mass remains unchanged across different celestial bodies.
🎥 Media Anchor & Pedagogical Scaffold
Mass vs Weight: Gravitational Forces Explained
Video Clip: Mass vs weight — gravitational field strength (g = 10 N/kg) and the W = mg formula (Runtime: 7m 33s).
🧠 1. Before Viewing (Activate & Predict)
If an astronaut weighs 80 kg on Earth, what is their mass on the Moon where gravity is only 1.6 N/kg?
👁️ 2. During Viewing (Watch With a Job)
- Distinguish: what is the difference between mass (kg) and weight (N)? Why do they have different units?
- Calculate: an object has a mass of 5 kg. What is its weight on Earth (g = 10 N/kg)? Show working.
- Predict: would your mass change on the Moon? Would your weight change? Explain the difference.
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Have students calculate their own weight force in Newtons on Earth, Moon, Mars, and Jupiter.
Immediate Task: Complete Worksheet 6: Mass vs Weight Solar System Calculation Matrix.
⚡ Whakaoho | Do Now: What Would You Weigh on the Moon?
Write down your answer — and write down your mass as well.
Two minutes: which of those two numbers changed when you went to the Moon, and which did not? If you wrote the same value for both, you have just located the exact thing this lesson fixes.
📖 Activity 1: Three Worlds, One Mass
Calculate across the solar system (13 min). Using Fg = m g, find your weight on Earth (g ≈ 9.8 N/kg), the Moon (≈ 1.6 N/kg) and Mars (≈ 3.7 N/kg). Your mass is the same number in all three. Only g moves.
Then explain it (12 min). Write the difference in your own words: mass is how much matter there is, weight is the force pulling on it. Then take the trap question — an astronaut floating in orbit. Has their mass changed? Has their weight changed? Are they genuinely weightless, or is something else going on?
📝 Activity 2: Year 10 Physics Worksheet & Explanation Scaffolding (20 mins)
Logbook Section 6. Record: (1) your weight on three bodies with working and units; (2) your own explanation of mass against weight; (3) your answer to the astronaut question with reasoning — and note honestly whether you changed your mind partway through writing it.
🏫 Kaiako Planning & Pedagogy Notes
Year 10 Curriculum Alignment: NZ Curriculum Phase 4 Science — Physical World strand. Builds foundational physics problem-solving skills for NCEA Level 1 Mechanics and Level 2 Physics.