1. Holt Physics Chapter 4 Section 4 Pages 141-148
Everyday Forces
Holt Physics
Chapter 4 Section 4
Pages

2. Everyday Forces
Weight – the magnitude of the force of gravity acting on an object

3. Fg = mg * Mass ≠ Weight Everyday Forces
Fg = force due to gravity (in Newtons)
m = mass of object (in kilograms)
g = acceleration due to gravity (-9.81 m/s2)
* Mass ≠ Weight

4. Everyday Forces
Normal Force – (Fn) – a contact force exerted by one object on another in a direction perpendicular to the surface of contact. On a horizontal surface, Fn = mg

5. Everyday Forces
Normal force diagrams-

6. Everyday Forces
Frictional Forces – Contact forces which oppose applied forces
These are the surfaces in contact at a microscopic level.

7. Everyday Forces 1. Static friction - (Fs) - force exerted
on a motionless object by the
environment to
resist an
external force
attempting to
cause a change
in motion

8. Everyday Forces 2. Kinetic friction – (Fk) – force
exerted on a moving object that
opposes
motion

9. Everyday Forces
* Fk < Fs due to surface adhesion between two surfaces in contact
Coefficient of friction (μ) – a ratio of frictional force to normal force between two objects

10. Coefficient of Friction
The coefficient of friction is a ratio of force of friction to the normal force acting between two objects.
This completely depends on the objects in contact.
Different experimental values have been calculated based on the materials in contact (page 144: table 4-2)

11. Coefficient of Friction Equations
Coefficient of static friction
μs = Fs,max Fn
Coefficient of kinetic friction
μk = Fk

12. Everyday Forces 3. Air resistance is a form of friction  as velocity
increases so does
air resistance