# Ipc definition: a push or a pull exerted on some object

 Sana 10.01.2019 Hajmi 1.75 Mb.

• ## Contact Forces: Result from physical contact between two objects

• Examples: Pushing a cart, Pulling suitcase
• ## Field Forces: Forces that do not involve physical contact

• Examples: Gravity, Electric/Magnetic Force

• ## The Law of Inertia

• An object at rest remains at rest, and an object in motion continues in motion with constant velocity (constant speed in straight line) unless the object experiences a net external force
• The tendency of an object not to accelerate is called inertia

• ## A crate is pulled to the right with a force of 82.0 N, to the left with a force of 115 N, upward with a force of 565 N and downward with a force of 236 N.

• A. Find the net external force in the x direction
• B. Find the net external force in the y direction
• C. Find the magnitude and direction of the net external force on the crate.

• ## To calculate Fnet, we need m and a

• M=2.0 kg
• What is a?
• Vi= 0 m/s, t=0.50 s,
• displacement=85 cm=.85 m
• Welcome back kinematic equations! 

• ## Friction Force= Ff

• Opposes applied force
• There are two types of friction: static and kinetic

• ## A 25 kg chair initially at rest on a horizontal floor requires a 365 N horizontal force to set it in motion. Once the char is in motion, a 327 N horizontal force keeps it moving at a constant velocity.

• A. Find coefficient of static friction
• B. Find coefficient of kinetic friction

• ## That means the forces in the x direction have to cancel out and the forces in y direction have to cancel out

• Fk = Fapp,x
• FN + Fapp,y = Fg
• NOTICE THAT NORMAL FORCE DOES NOT EQUAL WEIGHT IN THIS SITUATION

• ## Is box accelerating in y direction?

• No. Therefore Fnet in y direction is 0
• So FN + Fapp,y = Fg
• So FN = Fg- Fapp,y= 925 N- 325sin(25)
• FN= 787.65 N

• ## Is box accelerating in x direction?

• Yes. Therefore Fnet,x is not 0
• Fnet,x= Fapp,x – Ff
• Fapp,x = Fappcos(25)=294.6 N
• Use coefficient of friction to find Ff
• Ff=μFN=(0.25)(787N)=197 N

• ## Is box accelerating in y direction?

• No. Therefore Fnet in y direction is 0
• So FN = Fapp,y + Fg
• So FN = 485sin(35) + 319 N= 598 N

• ## What is the force that makes the object slide down the inclined plane?

• Gravity…but only in the x direction

• Fg,x = Ff
• ## If the box is accelerating

• Fnet= Fg,x - Ff

• ## If the object is in equilibrium then

• Fapp= Fg,x + Ff

• ## The block is in equilibrium so…

• Fnet=0
• Fg,y= FN=mgcosθ=(5.4kg)(9.81)cos(15)
• FN=51 N

• ## A 75 kg box slides down a 25.0° ramp with an acceleration of 3.60 m/s2.

• Find the μk between the box and the ramp
• What acceleration would a 175 kg box have on this ramp?

• ## So Fnet= ma= 75kg x 3.60 m/s2

• Fnet= 270 N

• ## We are trying to solve for μk

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