1. Chapter 5 Section 2 - 3
Forces

2. Forces Force – a push or pull on an object English Units Pound (lb)
SI Units
Newton (N)

3. More than one force acting on an object
Net Force – the sum of all the forces acting on an object
Balanced Force – forces are equal but opposite, causes no change in motion to object
Unbalanced Force – forces are unequal, causes a change in motion to object

4. Affect on Motion A balanced force is applied on a stationary object
Object will not move
An unbalanced force is applied on a stationary object
Object will start to move in the direction of the unbalanced force
A balanced force is applied on a moving object
Object will not change its motion
An unbalanced force is applied on a moving object
Object will change its motion in the direction of the unbalanced force

5. The Most Important Statement in Physics!
Unbalanced forces cause
acceleration.

6. Free Body Diagram Used to find net forces on objects
Draw a box to represent object
Draw arrows to represent direction of force
Label arrows with the force
Find the net force

7. Free Body Diagrams
15N
10N
15N – 10N= 5N right

8. Calculating Net Force
Change direction to positives and negative signs

9. Friction Friction – a force that opposes motion
(opposite direction)
Source – bumps and grooves in surface of objects
Factors that effect friction
Roughness of surface
Force pushing surfaces together
(more force pushes bumps and grooves together)

10. 2 Types of Friction
Static Friction – friction on a stationary object when a force is applied
(balanced force)
Kinetic Friction – friction on a moving object
(can be balanced or unbalanced based on the net force between the applied force and friction)
Sliding – when one surface slides past another
Rolling – when one surface rolls over another
Fluid – when particles of a liquid or gas collide with the surface of an object

11. Ways to Reduce Friction
Lubricants (oil, grease, air)
Switching from sliding kinetic friction to rolling kinetic friction (add wheels, ball bearings etc…)
Make surfaces smoother (polish the surfaces)
Reduce the force pushing surfaces together

12. Ways to Increase Friction
Make surface rougher (adding sand to ice)
- use a textured surface like a scouring pad to clean pots or gloves for baseball
Increase the force pushing the surfaces together