Physics 11

Mr. Jean

March 21st, 2012

The plan:

• Video clip of the day

• Mass & Weight Solutions

• Force Diagrams

Solutions:

• P. 137

• Questions 1-4

Free Body Diagrams:

• VERY IMPORTANT: Free-body diagrams are diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation.

• These diagrams will be used throughout our study of physics.

Free Body Diagrams (FBD):

• 1) Start with the object of interest. – Place a rectangle at the center of your

page to represent this object.

• 2) Lay out all forces being experienced by the object. – Draw neat straight lines representing

the forces.

• 3) List variables on the right hand side so people reading your diagrams know what you are talking about.

Key pieces to a FBD

• Let’s create a force diagram for the picture of Wile E. Coyote.

• Let’s create a force diagram for the picture of Road Runner.

FBD – Try this one: • A car is traveling on a level surface

heading east and it begins to slow down.

FBD – Try this one: • A car is traveling on a level surface

heading east and it begins to slow down.

Force diagrams to try:

• http://www.physicsclassroom.com/class/newtlaws/u2l2c.cfm

• Try Questions– A to D

Normal Force:

• The normal force is the component, perpendicular to the surface of contact.

• Example: the surface of a floor is preventing the object from penetrating the surface. The floor supplies the normal force.

Surface Friction:

• The magnitude of the force of surface friction is the product of the coefficient of friction and the magnitude of the normal force.

• The direction of the force of friction is always opposite to the direction of the motion.

Surface Friction:

Frictional Forces:• Example #1: An 80kg student is dragged across the floor.

The coefficient of friction between the floor and the student is 0.3.

• A) Draw a force diagram representing this situation.

Frictional Forces:• Example #1: An 80kg student is dragged across the floor.

The coefficient of friction between the floor and the student is 0.3.

• A) Draw a force diagram representing this situation.

Frictional Forces:• Example #1: An 80kg student is dragged across the

floor. The coefficient of friction between the floor and the student is 0.3.

A) Draw a force diagram representing this situation. B) What is the force of friction?C) What force is required to move the student?D) What is the students acceleration if 300N of force are

applied to them?

Frictional Forces:• Example #1: An 80kg student is dragged across the floor.

The coefficient of friction between the floor and the student is 0.3.

• A) Draw a force diagram representing this situation.

Frictional Forces:Example Question: An 80kg student is

dragged across the floor. The coefficient of friction between the floor and the student is 0.3. Calculate the following:

B) What is the force of friction?

Frictional Forces:Example Question: An 80kg student is

dragged across the floor. The coefficient of friction between the floor and the student is 0.3. Calculate the following:

B) What is the force of friction?

Frictional Forces:• An 80kg student is dragged across the floor. The

coefficient of friction between the floor and the student is 0.3. Calculate the following:

C) What force is required to move the student?

Frictional Forces:• An 80kg student is dragged across the floor. The

coefficient of friction between the floor and the student is 0.3. Calculate the following:

C) What force is required to move the student?

Frictional Forces:• An 80kg student is dragged across the floor. The

coefficient of friction between the floor and the student is 0.3. Calculate the following:

D) What is the students acceleration if 300N of force are applied to them?

Frictional Forces:• An 80kg student is dragged across the floor. The

coefficient of friction between the floor and the student is 0.3. Calculate the following:

D) What is the students acceleration if 300N of force are applied to them?

Frictional Forces:• Example #2: The force of friction experience by an

object is 255N. The object has a weight of 300N.

• 1) What is the coefficient of friction?

• 2) What is the objects acceleration if 500N of force are applied to the object?

Frictional Forces:• Example #2: The force of friction experience by an

object is 255N. The object has a weight of 300N.

• 1) What is the coefficient of friction?

• 2) What is the objects acceleration if 500N of force are applied to the object?

Situation:

Questions:

Using the image of Wile E. Coyote, determine the following values.

• 1) What is the coefficient of friction?

• 2) What is the mass of the rocket & Wile E.?

• 3) What is the acceleration of Wile E.?