Free-Body DiagramsOctober 31, 2013

Thursday, 10/31

Happy Halloween!

Use your notes to solve the following:1. Find the weights of these objects:

1. 1800 kg car 2. 0.12 kg baseball

Upcoming Events:• Open note quiz – Wednesday, 11/6• Unit 4 Test – Wednesday, 11/12

Unit 4: ForcesFree-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

Unit 4: ForcesFree-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

Unit 4: ForcesFree-Body Diagrams

Steps for drawing Free-body diagrams1. Replace the object with a dot or box.2. Identify all the long-range forces acting on the

object (ex. Gravity) 3. 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

Unit 4: ForcesFree-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.

Example 1: A book is at rest on a tabletop

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

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

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

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-