1. Forces and Newton’s Laws of Motion
Everyday Forces

2. Weight Weight – magnitude of the force of gravity acting on an object
Fg or w
Fg = mg
Force of gravity = mass * free-fall acceleration
Changes based on gravity
On Earth -9.81m/s2
Local variations of gravity
Gravity decreases as altitude increases
Gravity decreases as latitude decreases
scalar, magnitude of force only

3. The Normal Force
Normal force – a force exerted by one object on another in a direction perpendicular to the surface of contact
Often, but not always, opposes gravity Fn
For objects at an angle, Fn can be calculated by the following equation
Fn =-mg(cosθ)

4. Force of Friction Friction opposes motion
Friction also opposes any applied force
Static friction – the resistive force that opposes the relative motion of two contacting surfaces that are at rest with respect to one another
Friction involving stationary objects Fs
As long as the object that the applied force is acting on does not move Fs = -Fapplied
When the applied force is as great as it can be without causing movement, static friction is at its maximum value (Fs,max)

5. Force of Friction
Kinetic friction – the resistive force that opposes the relative motion of two contacting surfaces that are moving past one another
Friction involving moving objects Fk
Net external force acting on an object is equal to Fapplied-Fk
Caused by adhesion due to electrostatic forces between molecules

6. Force of Friction Friction is proportional to normal force
Easier to over come friction for less massive objects than more massive objects
Friction depends on the surfaces in contact
The more smooth the object, the less friction
Coefficient of friction – the ratio of the force of friction to the normal force acting between the two objects
Greek letter mu (µ)

7. Force of Friction To calculate coefficient of kinetic friction
µk=Fk/Fn
To calculate coefficient of static friction
µs=Fs,max/Fn
To calculate frictional force
Ff= µFn

8. Force of Friction Air resistance is a form of friction
Act on an object in the opposite direction of movement
Falling objects also experience air resistance
As velocity increases, resistance also increases
Terminal speed - when the upward force of air resistance balances the downward force due to gravity

9. Fundamental Forces
The universe has four fundamental forces or interactions
Gravitational force, electromagnetic force, weak nuclear force (or weak interaction), strong nuclear (or just strong force) (in order of weakest to strongest)
They are all field forces
At the macroscopic we can only observe gravitational and electromagnetic forces

10. Fundamental Forces Strong force holds the nucleus together.
It also holds the quarks together that makeup protons and neutrons
Weak interaction produces nuclear instability
Too much weak interaction causes a nucleus to undergo beta decay
Electromagnetic force – binds the electron to the nucleus as well as binds atoms and ions together to form compounds and molecules
Gravitational force – attracts masses together
Really only noticeable if one object is planet or moon sized, and even then, it is only noticeable at short distances