Circular Motion PDF QCAA Year 12

CIRCULAR MOTION UNIT 3 PHYSICS QCAA YEAR 12 LEARNING GOALS Circular motion ∙ describe uniform circular motion in terms of a force acting on an object in a perpendicular direction to the velocity of the object ∙ define the concepts of average speed and period ∙ solve problems involvin...

CIRCULAR MOTION UNIT 3 PHYSICS QCAA YEAR 12 LEARNING GOALS Circular motion ∙ describe uniform circular motion in terms of a force acting on an object in a perpendicular direction to the velocity of the object ∙ define the concepts of average speed and period ∙ solve problems involving average speed of objects undergoing uniform circular motion ∙ define the terms centripetal acceleration and centripetal force ∙ solve problems involving forces acting on objects in uniform circular motion. Limited to uniform circular motion!! COLLINS TYPE 1 List at least 6 examples of circular motion in every day life MOTION IN A CIRCLE When an object moves with a constant speed in a circle, its changing three quantities Direction of motion Angle from starting position Distance from starting point  Copy DESCRIBING CIRCULAR MOTION whole slide A is a point of the circumference of a circle Radius r Point A is moving at a velocity v in a anticlockwise direction. If A moves to A’ in a time t, it moves through an angle Δθ The distance travelled by the object is the arc of the circle moved in time t  Recall distance is a scalar quantity and so the total path around the circle is given as a distance. This distance over time is the speed of the object Question Does an object travelling at a constant speed around a circle have a constant velocity? PERIOD AND FREQUENCY  Particular note is rpm UNITS OF CIRCULAR MOTION remember this one EXAMPLE CONDITIONS FOR UNIFORM CIRCULAR MOTION Motion around a circle at a constant speed The velocity will constantly change as direction is constantly changing Since an object moving in a circle starts an finishes at the same point, its displacement is zero, so its average velocity is zero. MODULE 4.1 DO QUESTIONS 2,4-8  ANSWERS If you are stuck there are unit 3 solutions available on Moodle. Any mistakes in the solutions, let Dr Matherson know.  CENTRIPETAL FORCE MODULE 4.2 Consider spinning an object around on a piece of rope. What happens if you let go? Which direction does the object move in? Draw a diagram to represent this To keep going around in a circle, what force is needed? https://www.youtube.com/watch?v=KvC ezk9DJfk CENTRIPETAL FORCE To maintain circular motion, a force towards the centre of the circle is needed This is called Centripetal force Centripetal means centre seeking  CENTRIPETAL ACCELERATION CENTRIPETAL FORCE EXAMPLES OF CENTRIPETAL FORCE: TURNING A CORNER Turning a corner, the tyres exert a frictional force on the road towards the right of the car’s motion. The road also exerts a force on the tyres in the opposite direction causing the tyres (and car) to move to the left. If the force from the tyres is greater than the force from the road, the car will lose grip, no opposing force from the road so the car will go straight (skid).  PLAYING CORNERS As a passenger, when the car turns, it feels like you are being pushed outwards. This is often, incorrectly called “centrifugal force” Centrifugal means centre fleeing You are actually just continuing in a straight line (or trying to).  ORBITS (MORE ON THIS IN CHAPTER 6) The earth pulls on the moon at right angles to the moon’s velocity. This gravitational pull causes the moon to continually change direction thus circling or orbiting the earth. If the earth suddenly disappeared, the moon would move in a straight line with a constant speed (as per Newton’s first law).  MEASURING CIRCULAR MOTION  MODULE 4.2 QUESTIONS 7-10 Further questions available in the end of chapter review