Transcript newtons laws

Forces in One Dimension
Chapter 4
Physics Principles and Problems
Zitzewitz, Elliot, Haase, Harper,
Herzog, Nelson, Nelson, Schuler and
Zorn
McGraw Hill, 2005
Force - a push or pull on an object
http://farm2.static.flickr.com/1094/1276432131_53051d9a4f_o.jpg
http://www.deepocean.net/deepocean/pictures/science/basicphysics/apple2.jpg
“The Force is what gives a Jedi his power. It’s an energy
field created by all living things. It surrounds us,
penetrates us, and binds the galaxy together”
-Obi-Wan Kenobi-
http://old-wizard.com/wp-content/uploads/2008/06/darth.jpg
http://lh3.ggpht.com/haymansbeard/RrFkGaI8arI/AAAAAAAAAI4
/QdCbNRmw-ag/s512/Obi+Wan+Kenobi+01+Large.JPG
Force is a vector quantity, therefore it has
direction and magnitude.
http://www.ux1.eiu.edu/~cfadd/1150/04Nwtn/Images/crate1.gif
http://www.swe.org/iac/images/free_body.jpg
A free-body diagram is a model which represents all the
forces acting on a system.
In this video the system is the book, while the
agent is the hand pushing the book. Don’t forget,
gravity is also acting as a force, what then is
preventing the book from falling down?
http://www.batesville.k12.in.us/physics/PhyNet/Mechanics/Energy/Images/PushBookAnim.gif
Net Force = vector sum of all the forces
acting on an object.
http://id.mind.net/~zona/mstm/physics/mechanics/forces/netForce/netf3.gif
http://id.mind.net/~zona/mstm/physics/mechanics/forces/netForce/netf
You and your friend are pushing a stalled car. Your friend applies
230N of force while you apply 330N of force in the same
direction.
• What is the net force on the car?
• If you push in opposite directions what is the net force on the
car?
Newton’s Second Law of Motion
The rate of acceleration of an object is directly
related to the mass of the object and the net
force applied to the object.
• a = Fnet / m or
Fnet = ma
• 1 Newton = the
force required
to accelerate a
1 kg by 1m/s2
(N = kg•m/s2)
http://www.gaston.k12.nc.us/resources/teachers/webquests/Art/webquest/resour1.jpg
Remember, a is directly related to the Fnet
applied to the object and the m of the object.
http://drbonesshow.com/images-m1/m1m2.jpg
How much force is applied in both of these
examples?
http://www.k12.nf.ca/gc/Science/Physics3204/Projects2003/SlotA/ProjectA2/mud1.jpg
http://www.starbaseca.org/images/mud2.jpg
• What observations can we make?
Using Fnet = ma to explain freefall
• Since the
force acting
upon the
more
massive
object is
greater the
a is always
equal!
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/newtlaws/u2l3e2.gif
Newton’s First Law of Motion
An object at rest will remain at rest and an object
that is moving will continue to move in a straight
line with constant speed, if and only if the net force
acting upon that object is zero.
http://www.cooperativeindividualism.org/calvin-on-scientific-law.gif
Name all the forces acting upon these systems.
Which systems have zero net force? Remember
when Fnet = 0 then a = 0 (but it can still have v)!
• A book sitting on a table.
• A ball thrown horizontally on earth.
• A car driving at a constant velocity on the
highway.
• A ball thrown horizontally in space.
• A ball rolling on the ground.
• An elevator ascending up the 12th floor.
An object is at equilibrium if its net force is equal to zero.
Inertia - the tendency for an object to
resist change.
http://ircamera.as.arizona.edu/NatSci102/NatSci102/movies/law1_an.gif
• Why do you fall backward on the subway
when the train takes off?
• Why do you fall forward on the subway when
the train stops?