Understanding forces
A free-body diagram is a simple diagram that
shows the size and direction of all the forces
acting on an object
FNormal
FApplied
FFriction
p
FGravity
Force
Applied
• Force causing the object to move
• Opposite the force of friction
Force of
Friction
• Force causing the object to slow
down
Force of
Gravity
• The weight of the object on the
ground
Normal
Force
• Force applied to the object from
the ground
• Opposite the force applied
• Opposite the normal force
• Opposite the force of gravity
Read the Problem
Determine all the forces that
are acting on the object
Determine the direction that
each force is acting

Draw the object as a box

Draw each force as an arrow

Attach each arrow to the box

Aim the tip of each arrow in the
direction the force is acting

Label each arrow

A radio sits on a bookshelf. Observe the
forces acting on the radio
 Remember
◦ Read the Problem
◦ Determine all the forces
that are acting on the
object
◦ Determine the direction
that each force is acting

Remember
◦ The force of gravity acts on
the radio
 The direction is downward
◦ The force of the bookshelf
holds up the radio
 The direction is upward
The Free-Body Diagram will look like this
FNormal
FGravity

A car traveling down a road. Observe the
forces acting on the car.




The force of gravity acts on the car
downward
The force of the road holds the car upward
The force of the engine moves the car
forward
The Friction against the wheels and the
road pull backwards
The Free-Body Diagram will look like this
FNormal
FFriction
FEngine
FGravity
Finish the worksheet in groups. Remember the
strategies and steps for constructing a freebody diagram