P81 G

Slide 1: What links these images? IGCSE Physics – P8 Gravity

Slide 2: And these physicists? Aristotle Galileo Einstein Newton IGCSE Physics – P8 Gravity

Slide 3: Gravity is A. The force that holds the particles in a nucleus together B. The force you get when an object moves through air C. The force that exists between all objects with mass  D. The force you get between two charged objects IGCSE Physics – P8 Gravity

Slide 4: Lesson Aims 1. Appreciate that gravity is a force which acts between bodies even though they are not in contact. 2. Know that the Earth is a source of a gravitational field. 3. Appreciate the distinction between mass and weight. 4. Measure the acceleration due to gravity on Earth. IGCSE Physics – P8 Gravity

Slide 5: The force of gravity is A. Attractive always  B. Repulsive always C. Attractive and repulsive D. Always with you IGCSE Physics – P8 Gravity

Slide 6: Contact forces and action at a distance If two objects or materials need to be touching for the force to have an effect then it is a contact force. Examples: Friction Air resistance Is Gravity a contact force? No Gravity acts over a distance;- The force of gravity is said to be ACTION AT A DISTANCE IGCSE Physics – P8 Gravity

Slide 7: Mass and weight What is the difference between mass and weight? Mass Weight Mass is a measure of the Weight is the force of gravity amount of “stuff” or number of acting on an object. It changes particles which an object is depending on the strength of the made of. This remains constant gravitational field it is placed in. wherever it is in the universe On Earth the weight of a 1 kg mass = 10 N 1kg Mass = 1kg Weight = 10 N IGCSE Physics – P8 Gravity

Slide 8: Gravitational field strength; g On Earth the weight of a 1 kg mass = 10 N W g = gravitational field strength / N/kg g W = weight / N m m = mass / kg 1. How big is the value of g on Earth 2. What is the weight of a (i) 50 g (g for gram) eraser and (ii) a 67 Kg student on Earth. 3. What is the mass of a (i) pencil which weighs 0.2 N and (ii) and student who weighs 550 N on Earth. IGCSE Physics – P8 Gravity

Slide 9: Experiment P8(c) Measure either the mass or the weight of the following objects. then calculate the other one to complete the table. Object Mass / kg Weight / N Pencil case Eraser Pencil case Calculator Your self Two more things of your choice IGCSE Physics – P8 Gravity

Slide 10: On the moon Explain why an astronaut with a total mass > 120 kg can move so easily on the moon? IGCSE Physics – P8 Gravity

Slide 11: g on the moon = 1/6 g on Earth 1. How big is the value of g on the Moon 2. What is the weight of a (i) 50 g (g for gram) eraser and (ii) a 67 Kg student on the Moon? 3. What is the mass of a (i) pencil which weighs 0.2 N and (ii) and student who weighs 550 N on the Moon? IGCSE Physics – P8 Gravity

Slide 12: Galileo v Aristotle The larger the mass the quicker it accelerates. Nonsense; all masses accelerate at the same rate Who was correct? IGCSE Physics – P8 Gravity

Slide 13: The proof ……..finally IGCSE Physics – P8 Gravity

Slide 14: The size of ‘g’ on Earth by freefall S Sheet P8(B) Use S = ½ g t2 IGCSE Physics – P8 Gravity

Slide 15: Recording data Use S = ½ g t2 Height/m Time/s g /m/s2 1.0 So g = ? 1.0 2S 1.0 g 2 1.0 1.0 t S = height Mean value of g = g = acceleration of gravity Compare with g = 9.81 m/s2 t = time taken IGCSE Physics – P8 Gravity

Slide 16: Plenary 1. Write down 5 things you have learnt today 2. Share these with the person sitting next to you 3. Write down 2 things you want to know about gravity 4. Complete P8(D) 5. Duncan questions 1 – 4 on page 131 IGCSE Physics – P8 Gravity