DOC PREVIEW
UGA PHYS 1111 - notes5

This preview shows page 1-2-3 out of 9 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 9 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 9 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 9 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 9 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Chapter 5: Forces andNewton’s Laws of Motion Previously, we have studied kinematics, which- describes the motion of an object (x, v, a)- does not explain the cause of the motion Now, we begin the study of the second part ofmechanics – dynamics - which does address the cause of motion- that cause is a force, a push or pull Force, , is a vector, has magnitude and direction How forces affect the motion of an object is describedby Newton’s Laws of Motion (Newtonian Mechanics) Objects are treated as point particles; in Chapter 10 wewill consider the shape of an object in more detail € r FNewton’s First Law of Motion An object at rest will remain at rest An object moving at a constant velocity will continue tomove at the constant velocity, unless acted upon by a netforce What does it mean?- tendency for an object’s motion not to change Net force = the sum of all applied forces0321=++=∑iiFFFFrrrr- No effect on the motion € r F 1 € r F 2 € r F 3According to the 1st law, zero velocity (at rest) isequivalent to constant velocityAn object with a constant velocity does not require aforce to maintain its velocity- forces act to change motion, not to sustain themotion (e.g., the speed of the Voyagers)- seems contrary to everyday experience Inertia – tendency for an object to remain at rest, or toremain in motion with a constant velocity - all objects have inertia Mass – a quantitative measure of inertia (a scalar)- use symbol m - unit is kg (SI) or slug (British)- more mass, means more inertia- not equivalent to weight (a force)Newton’s Second Law of Motion If there is a net force, there is a change in velocity (anacceleration) € r F ii∑=r F ∑= mr a  1st law implies the 2nd law Meaning: if a net external force acts on an object ofmass m, it will be accelerated and the direction of theacceleration will be in the same direction as the netforce € r a =r F ∑mF1F2F3ΣFaDemo 8.2.2Eq. (5.1)All forces in Newton’s second law areexternal – a force exerted on an objectby some outside agentUnits: F=ma [mass][L/T2]->(kg)(m/s2)=N, Newton- The Newton is a derived unit- In British units, force is given by the lband mass is given by the slug-> slug=lb s2/ftThe Free Body Diagram (FBD) A schematic representation of an object and allthe external forces that act upon it Always draw in every problem!!!! From Newton’s 2nd law: € r F = mr a = 0∑r F G+r F table= 0r F table= −r F G € r F GtableFrBook atrest onthe tableFundamental Types of Forces1. Gravitational2. Electromagnetic – (electric and magnetic)3. Weak Nuclear4. Strong NuclearElectroweakWe will only consider the first twoGravitational ForceFrom our studies of free-fall motion and projectilemotion  gravity causes an object to accelerate in thenegative y-direction€ r a y= −g ˆ y yApply thesecond lawym € r F G= −mg √ y  This is only an approximation which holds only near thesurface of the Earth (as g is only constant near the surface).But a good approximation! We would like a more fundamental description of gravity- g is an empirical number- physicists don’t like empirical numbers This lead Newton to devise his Law of UniversalGravitation (the subject of Chapter 12(?))Example Problem Three forces acting on an object aregiven by =(-2.00 + 2.00 ) N, =(5.00– 3.00 ) N, and =-45.0 N. The objectexperiences an acceleration of magnitude3.75 m/s2. (a) What is the direction ofacceleration? (b) What is the mass of theobject? (c) If the object is initially at rest,what is its speed after 10.0 s? (d) Whatare the velocity components of the objectafter 10.0 s?€ i€ ˆ i € ˆ i € r F 1 € r F 2 € r F 3€ ˆ j € ˆ


View Full Document

UGA PHYS 1111 - notes5

Download notes5
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view notes5 and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view notes5 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?