lesson
Gravity changes the direction of orbital motion
1 · Learn
Gravity is an attractive interaction between masses. An orbiting object continually changes direction under gravity rather than moving in a straight line. A satellite in orbit is not beyond the reach of gravity.
Distinguish mass from weight and orbital motion from a supported object resting on a surface. Models may neglect resistance or other bodies; state these simplifications.
2 · Worked example
The Moon remains in orbit because Earth's gravity changes its direction of motion. Saying there is no gravity in space does not explain the orbit.
3 · Your turn
Why is 'a satellite orbits because gravity is absent' incorrect?
Check your answer
Gravity supplies the force changing its direction and keeping it in orbit.
4 · Apply your learning
Draw a model with an inward force and a separate direction-of-motion arrow, explaining that the arrows show different quantities.
Adult guidance and safety
Use supplied evidence and approved models. Practical science needs a qualified adult, appropriate equipment and a risk assessment. Do not attempt chemical reactions, heating, mains electricity or solar observation independently. Never request personal health or genetic disclosures.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
My observation notebook
Follow your teacher's approved method and safety instructions. Record the sample or supplied dataset, conditions, measurements with units and uncertainties where appropriate. Distinguish observations from explanations. A described experiment is not permission to carry it out; do not improvise equipment or invent missing results.
Ask your teacher for support with the method and recording. A prediction is what you think might happen; an observation is what you actually see, hear or feel safely.
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