updated physics chapter 9

Circular motion (ferris wheel example)- move in a circular motion as it revolves around a single axis, called the axis of rotation. For a ferris wheel the axis of rotation is a line perpendicular to the side of the wheel that passes through the wheels center

Tangential speed (Vt)- speed of an object in circular motion.

-the tangential speed of an object in circular motion is the objects speed along an imaginary line drawn tangent to the circular path

-when the tangential speed is constant (uniform circular motion) the motion is described as uniform circular motion

-tangential speed depends on difference

Ex: a horse on the outside of a merry-go-round has greater tangential speed because it covers more distance than the horses on the inside

Centripetal Acceleration (Ac)

-the acceleration of an object moving in a circular path and at constant speed due to a change in direction. (objects can accelerate when it changes speed, direction, or both)

-The acceleration of an object moving in a circular path is centripetal acceleration. CA must involve a change in the objects velocity

-Centripetal acceleration is always directed toward the center of a circle

Centripetal acceleration vs. tangential acceleration

-ex: car traveling in a circular track

-because the car is moving in a circle the car has a centripetal component of acceleration

-if the car's speed changes the car also has a tangential component of acceleration

Centripetal force (Fc)

-net force directed toward the center of a circle

-centripetal force is simply the name given to the net force on an object in uniform circular motion

-any type of force or combination of forces can provide this centripetal force

Ex: friction between a race cars tires and a circular track is a centripetal force that keeps the car in a circular path

-gravity is a centripetal force that keeps the moon in its orbit

-tension on a string attached to an object you are twirling overhead in a circle is another example of centripetal force

Centripetal force

-if the centripetal force vanishes the object stops moving in a circular path

Ex: a ball that is on the end of a string is whirled in a vertical circular path

Rotating system

-to better understand the motion of a rotating system consider a car traveling at high speed and approaching an exit ramp that curves to the left

-as the driver makes a sharp left turn the passenger slides to the right and hits the door. The passenger moves toward the door because of inertia

Gravitational Force

-Earth and many of the other planets in our solar system travel in nearly circular orbits around the sun

-a centripetal force must keep them in orbit

-one of isaac newtons discoveries was that this centripetal force is gravity

-orbiting objects are in free fall

Gravity

-the centripetal force that holds the planets in orbit is the same force that pulls an apple toward the ground- gravitational force or gravity (Fg)

-the force of gravity is the mutual force of attraction between particles of matter

-gravity depends on the masses and the distance between them

-gravity and weight are directly relates. As Fg increases, weight also increases

-the gravitational forces that two masses exert on each other are always equal in magnitude and opposite in direction

Short answer

Describe the difference between tangential and centripetal acceleration

-tangential acceleration means there was a change in speed in circular motion. Centripetal acceleration results only from a change in direction

What makes a passenger in a turning car slide toward the door

-Inertia makes a passenger slide towards the door

On a roller coaster what is the direction of the force that causes the coaster and its passengers to move in a circle. What provides this force?

-direction of force-toward the center of the loop

Example of centripetal acceleration but no tangential acceleration

-driver is moving in a circle at a constant speed

Can a car move around a circular racetrack so that the car has a tangential acceleration but no centripetal acceleration

-no since its moving in a circle, the car will always have a centripetal acceleration

Explain how gravity keeps a satellite in orbit

-the combination of the acceleration due to gravity and the tangential speed results in the satellite following a path that follows the curve of the earth

Is there gravitational force between two students sitting in a classroom

-Yes, but the force is very small because the mass of each student is small compares to the earths mass

Identify the influence of mass and distance on gravitational forces

-mass and distance are directly ties to gravity

If a satellite orbiting earth is in free fall why does the satellite not fall and crash into earth

-The satellite is in free fall but is also moving parallel to Earth (remember resolving into its vector components). Its speed is such that Earth's surface curves away from the orbit at the same rate that the satellite falls.

How does gravitational force exerted by earth on the sun compare with the gravitational force exerted by the sun on earth

-the forces are equal in magnitude and opposite in direction

Would you expect for tides to be higher at the equator or at the north pole

-equator because the center of the earth is where the moons gravitational force is at its highest point