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Transcript
Circular Motion Uniform circular motion: examples include •Objects in orbit (earth around the sun •Driving a car around a corner •Rotating a ball around on a string Circular Motion c Circular Motion According to Newton’s mechanics, objects don’t tend to move in a circle by themselves. They tend to either be at rest of move in a straight line at constant speed (this is Newton’s first law) Circular Motion Circular motion is not “natural” motion Something (a Force) must make an object move in a circle The Force causing circular motion can be one of many different forces, depends on the situation (orbit = gravitational force, car turning a corner = frictional force between tires and the road, ball on a string = tension force) Circular motion example Circular motion: car travelling around a corner F is friction Example of circular motion Now gravity is influencing circular motion Circular Motion Remember from Newton’s 2nd law, that …..Force = mass x acceleration (F = ma) But if the object is in uniform circular motion, their speed is constant, so is acceleration = 0? Circular Motion In circular motion, the acceleration is a change in the direction of the object, even though the speed is constant, the direction keeps changing, and velocity is a vector. The force keeps pulling the object to the center, hence we call this type of acceleration “centripetal” acceleration which means “center seeking”. Circular Motion Solving circular motion problems is like a typical “force” problem where the motion is circular rather than linear. F = ma still works, now we have a new term for centripetal acceleration ac = v2/r acceleration (centripetal) = velocity squared/radius. Uniform circular motion Centripetal acceleration Circular Motion Example ….. Ball on a string rotating horizontally Let’s say it’s a 1 kg ball rotating at 4 m/s at a radius of 0.5m. What is the Force of tension in the string? Find the acceleration of the ball where a = v2/r Using the idea that F=ma and that the Force causing circular motion is the tension in the string.