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CIE IGCSE Physics Turning Forces Circular Motion and Gravitational attraction Centripetal Force Recap of Forces The meaning of centripetal force The three factors on which centripetal force depends 1 2 3 Why an object moving in a circle has an inward acceleration Task Complete sheet on Terminal Velocity Centripetal Force CENTRIPETAL FORCE is the general name given to a centrally directed force that causes circular motion. Tension provides the CENTRIPETAL FORCE required by the hammer thrower. Other examples of centripetal force Situation Centripetal force Earth orbiting the Sun GRAVITY of the Sun Car going around a bend. FRICTION on the car’s tyres Airplane banking (turning) PUSH of air on the airplane’s wings Electron orbiting a nucleus ELECTROSTATIC attraction due to opposite charges Factors affecting centripetal force Centripetal force INCREASES if: - the object is moved FASTER - the object’s mass is INCREASED. - the radius of the circle is DECREASED. Centripetal Force Why does an object moving in a circle have an inward acceleration ? When an object moves in a circle, there is unbalanced force on it that acts towards the center of the circle. Newton 2 what happens if an object has an unbalanced force on it? Acceleration- How? Acceleration is the change in velocity / time Remember velocity is a vector – speed and direction So we have …….. What happens if the string breaks? What direction does the ball move? Remember Newton 1 String breaking quiz Draw on the diagram provided Tasks Do questions 1- 4 on page 49 Question 12 on page 51 Fill in missing words Choose appropriate words to fill in the gaps below: circular An object will only move along a __________ path if it is force constantly acted on by a centripetal _________. The force is towards always directed __________ the centre of the circular path. increases Centripetal force ___________ if the object moves in a smaller greater radius path or at a __________ speed. centripetal force is the Moon orbiting the An example of a _________ gravitational Earth due to the Earth’s _____________ pull on the Moon. WORD SELECTION: gravitational force greater circular towards centripetal increases Centripetal Force Recap of Forces The meaning of centripetal force The three factors on which centripetal force depends 1 2 3 Why an object moving in a circle has an inward acceleration Circular Motion Simulations Ladybug Revolution - PhET - Join the ladybug in an exploration of rotational motion. Rotate the merry-go-round to change its angle, or choose a constant angular velocity or angular acceleration. Explore how circular motion relates to the bug's x,y position, velocity, and acceleration using vectors or graphs. Motion in 2D - PhET - Learn about velocity and acceleration vectors. Move the ball with the mouse or let the simulation move the ball in four types of motion (2 types of linear, simple harmonic, circle). See the velocity and acceleration vectors change as the ball moves. Motion produced by a force - linear & circular cases - netfirms Uniform circular motion - Fendt Carousel - centripetal force - Fendt Relation between speed and centripetal force - NTNU Vertical circle & force vectors - NTNU Circular Motion & Centripetal Force - NTNU Inertia of a lead brick & Circular motion of a water glass - 'Whys Guy' Video Clip (3 mins) (2nd of 2 clips) Gravitational attraction • Gravity is an attractive force • Gravity depends on mass and the distance between objects. Gravitational field strength Gravitational field strength is equal to the force exerted on an object of mass 1kg. On the Earth’s surface the gravitational field strength is about 10 N/kg (okay 9.81 N/kg) Moon’s surface = 1.6 N/kg Mars’ surface = 3.7 N/kg Weight is the force of gravity on an object. Gravitational attraction Gravity is a force exerted by all objects on each other. Gravitational force: - is always attractive - increases if the mass of the objects is increased - decreases if the distance between the objects is increased – it is inversely proportional - P.S These are Sir Isaac Newton’s rules on Gravity Complete Answers Surface Field Strength (N/kg) Object mass (kg) Object weight (N) Earth 10 80 800 Moon 1.6 80 128 Mars 3.7 200 740 Jupiter 25 60 1500 Pluto 0.07 80 5.6 Choose appropriate words to fill in the gaps below: objects on each other Gravity is a force exerted by all ________ masses because of their ________. decreases if the distance between the Gravitational force __________ increases if their masses are objects is increased but __________ increased. weight _________ is the force of gravity on an object. On the Earth’s newtons surface an object of mass 1kg has a weight of 10 __________. The Moon’s gravity is about one sixth the strength of the mass Earth’s because its _________ is much lower. WORD SELECTION: increases newtons masses objects mass decreases weight Gravity Simulations Free-fall Lab - Explore Science Galileo Time of Fall Demonstration - 'Whys Guy' Video Clip (3 mins) - Time of fall independent of mass - Leads slug and feather with and without air resistance. (1st of 2 clips) Distance Proportional to Time of Fall Squared Demonstration - 'Whys Guy' Video Clip (3:30 mins) - Falling distance proportional to the time of fall squared. (2nd of 2 clips some microphone problems) Lunar Lander - PhET - Can you avoid the boulder field and land safely, just before your fuel runs out, as Neil Armstrong did in 1969? Our version of this classic video game accurately simulates the real motion of the lunar lander with the correct mass, thrust, fuel consumption rate, and lunar gravity. The real lunar lander is very hard to control. Moonlander Use your thrusters to overcome the effects of gravity and bring the moonlander safely down to earth. BBC KS3 Bitesize Revision: Mass and gravity Weight