Force: An action exerted on an object (a push or a pull) in order to change the state of rest or motion of an object. Measured in Newtons (N)

Free Body Diagrams Identifies all of the Forces acting on an objectIdentifies all of the Forces acting on an object Each Diagram has a Vector Arrow:Each Diagram has a Vector Arrow: Size of arrow: Shows the magnitude of the force Direction of arrow: Shows direction of force

2 Categories of Forces Contact Forces: things touching Each other At-a-distance Forces: things that don’t touch each other

Force of Gravity = F g The Earth pulls you downward Any object near Earth is under it’s pull

Force of Tension (F T ) Contact force acting through a string, chain, etc…

Force of Friction = F F Always goes in the opposite direction of motion (or the opposite direction an object would move)

Normal Force = F N The thing that pushes stuff up

Normal Force Surface Force that acts perpendicular to object Consider the following: 1.0 kg mass on a table –We know from Newton’s 3 rd law the table has to…. P ush upward with the same force –How does the block know? –What if it didn’t push hard enough? –What if it pushed too hard?

Normal Force (F N ) Reactive Force

Types of Forces PUT THESE IN YOUR BOOKY BOOK F g = Force of Gravity F A = Force Applied F T = Force of Tension F f = Force of Friction F N = Normal Force (“Support”)

Example: Book on Table F g force on book by the Earth Support force on book by table Fg FNFN Draw a circle around your object

Example: Continued 2) Block Moving1) Push Block3) Book stops

A cat is at rest on a table top. The free-body diagram for this situation is shown below:

A rightward force is applied to a Piano in order to move it across a desk at constant velocity. Consider frictional forces.

Force: An action exerted on an object (a push or a pull)An action exerted on an object (a push or a pull) in order to change the state of rest or motion of an object. Measured in Newtons (N)Measured in Newtons (N) Net Force: Combination of all the forces acting on an object. (add them up)

Balanced Forces If all of the pushes and pulls are even on an object, then the object “keeps on doing what it was doing” Tug-o-war Two teams that are evenly matched play tug- o-war NOTHING HAPPENS

Unbalanced Forces Unbalanced forces cause objects to change velocities Tug-o-war –Two teams that are unevenly matched play tug-o-war –One team will win

Unbalanced Force What happens when an object has an unbalanced force acted upon it? Unbalance forces cause acceleration!!

If the forces are… Balanced – –Nothing happens –Ex: A book sitting on a shelf Unbalanced – –The object changes what it is doing –Ex: pick something that is moving

A rightward force is applied to a plate in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance.

A rightward force is applied to a box in order to move it across a desk at constant velocity. Consider frictional forces. Neglect air resistance

A force is applied to the right to drag a sled across loosely-packed snow with a rightward acceleration.

What is wrong with the following? 1.An object at rest has no forces acting on it. 2.If an object is moving, the object must have a force acting on it or else it would stop. 3.If an object is traveling at a constant speed it needs to have a constant force applied.

Mass is the measure of the inertia of an object –The more mass an object has, the harder it is to move it (or stop it) Mass ≠ Weight changes due to gravity –You can be “weight-less” in space...but you’re not mass-less! Mass

Mass is a PROPERTY –Measured in kilograms (kg) Weight is a FORCE –Measured in newtons (N) Mass, Continued A force, in simple terms, is either a push or a pull

Newton’s 2 nd Law The acceleration of an object is directly proportional to the net force acting on the object and is inversely proportional to the mass of the object. In other words: F = mass x acceleration F = m a