1. Free-Body Diagrams
October 31, 2013

2. Use your notes to solve the following:
Thursday, 10/31
Happy Halloween!
Use your notes to solve the following:
Find the weights of these objects: kg car kg baseball
Upcoming Events:
Open note quiz – Wednesday, 11/6
Unit 4 Test – Wednesday, 11/12

3. Unit 4: Forces Free-Body Diagrams
Vector Review
A vector has magnitude and direction (ex. Velocity)
The magnitude of the vector quantifies how large it is.
Arrows are used to depict a vector (size and direction)
Force is a vector
Magnitude – amount of force in Newtons (N)
Direction is depicted with an arrow

4. Unit 4: Forces Free-Body Diagrams
Free Body Diagrams are…
Are a pictorial representation of forces acting on an object.
Are used to show the magnitude and direction of all forces acting on an object.
The size of the arrow reflects the size of the force
The arrow shows the direction the force is acting
Force is a vector
Magnitude – amount of force in Newtons (N)
Direction is depicted with an arrow

5. Unit 4: Forces Free-Body Diagrams
Steps for drawing Free-body diagrams
Replace the object with a dot or box.
Identify all the long-range forces acting on the object (ex. Gravity)
Identify all the contact forces acting on the object.
Remember that only something that is physically touching the object can apply a contact force
Possible types of contact forces – push, tension, normal, and friction

6. Unit 4: Forces Free-Body Diagrams
Things to remember when working with force diagrams:
Always follow all 3 steps
Force due to gravity acts on all objects and always points down
Force arrows must originate from the dot, this means that you will never have an arrow pointing at the dot, always away from the dot
Surfaces apply a normal force that is always perpendicular to the surface.

7. Example 1: A book is at rest on a tabletop

8. Example 2: A girl is suspended motionless from the ceiling by two ropes

9. Example 3: An egg is free-falling from a nest in a tree
Example 3: An egg is free-falling from a nest in a tree. Neglect air resistance.

10. Example 4: A Flying squirrel is gliding from a tree to the ground at a constant velocity. Consider air resistance.

11. Example 5: A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance. A free-