Force - a push or pull on an object

Types of Forces

• Gravity • Normal• Friction• Tension• Magnetic• Buoyant• Applied

“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-

Force is a vector quantity, therefore it has direction and magnitude.

A free-body diagram is a model which represents all the forces acting on a system.

Net Force = vector sum of all the forces acting on an object. (ΣF)

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 MotionThe 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)

Remember, a is directly related to the Fnet applied to the object and the m of the object.

How much force is applied in both of these examples?

Fnet = ma explains freefall

• The force acting upon the more massive object is greater, but a is always constant.

Newton’s First Law of MotionAn 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.

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.

• 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?

• Why does this motorcyclist continue to move after the motorcycle has stopped?

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+01+Large.JPG

5. http://1.bp.blogspot.com/_kEZuOyArlOk/TNEEtpFnx_I/AAAAAAAAA7s/JpHGl9jCTks/s1600/Forces.bmp6. http://www.ux1.eiu.edu/~cfadd/1150/04Nwtn/Images/crate1.gif7. http://www.swe.org/iac/images/free_body.jpg8. http://id.mind.net/~zona/mstm/physics/mechanics/forces/netForce/netf3.gif9. http://id.mind.net/~zona/mstm/physics/mechanics/forces/netForce/netf2.gif10. http://www.gaston.k12.nc.us/resources/teachers/webquests/Art/webquest/resour1.jpg11. http://drbonesshow.com/images-m1/m1m2.jpg12. http://www.k12.nf.ca/gc/Science/Physics3204/Projects2003/SlotA/ProjectA2/mud1.jpg13. http://www.starbaseca.org/images/mud2.jpg14. http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/newtlaws/u2l3e2.gif15. http://www.cooperativeindividualism.org/calvin-on-scientific-law.gif16. http://mitchellwest7.wikispaces.com/file/view/9028414.jpg/219002490/9028414.jpg