Physics I Honors Specific Forces Centripetal Force

Physics I Honors Warm up Planet Zonk is twice as far from the sun as Earth. What is its period? Herman the astronaut ( mass 80kg) is floating in orbit about earth and feels a gravitational attraction of 360 newtons. What is the value of gravity at his location? What is his orbital radius as a multiple of earth’s radius.

Physics I Honors Objectives · Explain why a body moving with uniform circular motion must be regarded as undergoing acceleration and state the direction of the acceleration. · Predict the path of an object which has a force acting on it perpendicular to the direction of its velocity. · Indicate the direction of the instantaneous velocity, centripetal acceleration, and centripetal force for an object moving at constant velocity in a circle. · Calculate centripetal acceleration and force.

Physics I Honors Imagine… Think about the moon on its journey around the earth… How about an amusement park ride that spins you around in a constant circle… How do you describe this kind of circular motion? Is the velocity constant or is it accelerating? How does the moon stay up there in the sky?

Physics I Honors What Is Uniform Circular Motion? Uniform Circular Motion is motion in a circle with: –Constant Radius R v – Constant Speed v = |v|

Physics I Honors What if the String Breaks?

Physics I Honors Centripetal Force Provides acceleration toward the center which causes an object to continually change velocity because it is changing direction while the speed remains constant. F c = ma c

Physics I Honors What happens when you turn.

Physics I Honors Without Centripetal Force

Physics I Honors With Centripetal Force

Physics I Honors Force is Perpendicular to the Velocity

Physics I Honors Check your understanding An object is moving in a clockwise direction around a circle at constant speed. Use your understanding of the concepts of velocity, acceleration, and force to answer the next five questions. Use the diagram shown at the right. A B C

Physics I Honors Vector 1 1. Which vector below represents the direction of the force vector when the object is located at point A on the circle?

Physics I Honors Vector 2 2. Which vector below represents the direction of the force vector when the object is located at point C on the circle?

Physics I Honors Vector 3 Which vector below represents the direction of the velocity vector when the object is located at point B on the circle?

Physics I Honors Vector 4 4. Which vector below represents the direction of the velocity vector when the object is located at point C on the circle?

Physics I Honors Vector 5 5. Which vector below represents the direction of the acceleration vector when the object is located at point B on the circle?

Physics I Honors Motion in a circle Velocity is a vector; it has direction An object travelling in a circle at constant speed is continuously changing direction Therefore, it is accelerating Thus, requires a force

Physics I Honors Centripetal Acceleration This acceleration can be calculated a c = v 2 / r a is the centripetal acceleration v is the speed r is the radius of the circle

Physics I Honors Circular Speed As speed is distance traveled divided by the time it takes to travel the distance v = 2  r/T v is the speed r is the radius of the circle T is the period of revolution

Physics I Honors Practice 1 A runner moving at a speed of 8.8 m/s rounds a bend with a radius of 25 m. What is the centripetal acceleration of the runner? 3.1 m/s 2 What provided this acceleration to the runner? friction between his shoes and the track

Physics I Honors Practice 2 Racing on a flat track, a car going 32 m/s rounds a curve 56 m in radius. What is the car’s centripetal acceleration? 18 m/s 2 What would be the minimum coefficient of static friction between tires and road that would be needed for the car to round the curve without skidding? 1.8

Physics I Honors Homework A/c # 6 and 7 Problems 13 to 20