Force in a circle

The Bucket of water• How does he not get wet?• What would happen if the handle snaps?

http://www.youtube.com/watch?v=EPWmGttDCNY&feature=related

Describe qualitatively motion in a curved path due to a perpendicular force, and understand the centripetal acceleration in the case of uniform motion in a circle

Express angular displacement in radians Recall and use centripetal acceleration

a = v2/r Apply the equation F = ma to uniform motion in

a circle to derive F = mv 2/r

Unit 1 Kinematics Section 3 Centripetal Motion ONE

Do Now:What is the centripetal acceleration of a lady bug sitting on the edge of a 10 cm diameter CD that spins at 1200 revolutions per minute?

Lesson 1 Objectives

In Class / HOMEWORK:Glencoe page155 – 156Example Problem 2Practice Problems: 12 – 15Section Review: 16, 19

What are the forces?centripetal” means “centre

seeking”. Centripetal is an adjective

describing the force; it is not the name of a special type of force, such as tension, gravity, magnetic force etc - e.g. pulling the bucket in with the rope

centrifugal, or centre-fleeing e.g. the force of the bucket on my hand

Planetary orbits (almost!) gravitation

Electron orbits electrostatic force on electron

Centrifuge contact force (reaction) at the walls

Gramophone needle the walls of the groove in the record

Car cornering friction between road and tyres

Car cornering on banked track component of gravity

Aircraft banking horizontal component of lift on the wings

Lesson 1

Newton's 3rd law….

Every force has an equal and opposite reaction, so the force produced from the air, pushes the balloon in the opposite direction

Lesson 1

A force cannot exist on its own – there is always a second force acting against it.

This forms the basis of Newton’s third law of motion states, which states:

What is Newton’s third law?

These pairs of forces that act between two objects are sometimes called action–reaction pairs.

If object A exerts a force on object B, then object B exerts an equal but opposite force on object A.

Lesson 1

Centrifugal and Centripetal Force

• The centripetal force is directed inward, towards the axis of rotation

• As you swing the ball with the string, you feel the string tug on you hand...., this is called the centripetal force and is equal and opposite to the centrifugal force...

Lesson 2DO NOW:A 40.0 gram rock is whirled horizontally at the end of a 0.60 meter string with a velocity of 2.20 m/s..

What is the TENSION (force) on the string?

HOMEWORK:Page: 166-167 #’s 63, 64, 65, 67

The difference between linear and angular velocity

• The instantaneous linear velocity at a point in the circle is usually given the letter v and measured in metres per second (m s-1).

• The angular velocity is the angle through which the radius to this point on the circle turns in one second. This is usually given the letter w  (Greek omega) and is measured in radians per second (rad s-1)

http://www.animations.physics.unsw.edu.au/jw/circular.htmLesson 2

The important formulas

a= v2 / r

F = Force (newtons)V = Velocity (m/s)r = Radius (m)m = Mass (kg)w = radial velocity rad s-1

F = m v w = m w2 r

Plenary - Answer This Question

You are sitting in the seat of a rollercoaster. Your mass is 50.0kg and the mass of the rollercoaster is 1000.0kg. You are travelling at a speed of 20.00 m/s. The centripetal force acting on you is 1000.N. What is the radius of the ‘loop the loop’ you are travelling around?