Forces and Newton’s Laws of Motion

Everyday Forces

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 ______

On Earth 9.81m/s2
–Local variations of gravity
Gravity ______as altitude increases
Gravity ______as latitude decreases

–Scalar, magnitude of force only

The Normal Force

Normal force – a force exerted by one object on another in a direction ______to the surface of contact

Often, but not always, ______gravity

Fn

For objects at an ______, Fn can be calculated by the following equation

Fn = - mg(cosθ)

Force of Friction

Friction opposes ______

______also opposes any applied force

______friction – the resistive force that opposes the relative motion of two contacting surfaces that are at rest with respect to one another

–Friction involving ______objects

–Fs

–As long as the object that the ______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 ______(Fs,max)

______friction – the resistive force that opposes the relative motion of two contacting surfaces that are moving past one another

–Friction involving ______objects

–Fk

–______acting on an object is equal to Fapplied-Fk

–Caused by adhesion due to electrostatic forces between ______

Friction is ______to normal force

–Easier to over come ______for less massive objects than more massive objects

Friction depends on the surfaces in contact

–The more ______the object, the less fricition

–______– the ratio of the force of friction to the normal force acting between the two objects

Greek letter mu (µ)

To calculate ______of kinetic friction

–µk=Fk/Fn

To calculate coefficient of ______friction

–µs=Fs,max/Fn

To calculate frictional force

–Ff= µFn

______is a form of friction

–FR

–Acts on an object in the opposite direction of movement

Falling objects also experience ______

–As velocity increases, ______also increases

–______- when the upward force of air resistance balances the downward force due to gravity

Fundamental Forces

The universe has four fundamental forces or interactions

oGravitational force, electromagnetic force, weak nuclear force (or weak interaction), strong nuclear (or just strong force) (in order of weakest to strongest)

oThey are all field forces

At the macroscopic we can only observe gravitational and electromagnetic forces

Strong force holds the nucleus together.

oIt also holds the quarks together that makeup protons and neutrons

Weak interaction produces nuclear instability

oToo 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

oReally only noticeable if one object is planet or moon sized, and even then, it is only noticeable at short distances