Review- What is Review- What is happening in this video?happening in this video?

How? How?

http://player.discoveryeducation.com/index.cfm?guidAssetId=69D515CC-CFDF-4DB2-9F6D-http://player.discoveryeducation.com/index.cfm?guidAssetId=69D515CC-CFDF-4DB2-9F6D-386F68CD4E02&blnFromSearch=1&productcode=US#386F68CD4E02&blnFromSearch=1&productcode=US#

ObjectivesObjectives

Review- Entrance Ticket. Review- Entrance Ticket.

Weight Vs. Mass Weight Vs. Mass

Distinguish between force and net Distinguish between force and net force.force.

Equilibrium rule.Equilibrium rule.

Weight Weight VS. VS. MASSMASS

Force of gravity acting Force of gravity acting on an objecton an object

http://http://www.exploratorium.edwww.exploratorium.edu/ronh/weight/u/ronh/weight/index.htmlindex.html

Amount of Matter an Amount of Matter an object containsobject contains

What is Force?What is Force?

Force is a Push or a PullForce is a Push or a Pull Forces are Forces are vector quantitiesvector quantities - they have a - they have a

magnitude (How Much) and a directionmagnitude (How Much) and a directionEx.: 10 N to the rightEx.: 10 N to the right

Forces are shown with arrowsForces are shown with arrowsPoint in the direction which it is being applied.Point in the direction which it is being applied.

The length of the arrow shows the magnitude The length of the arrow shows the magnitude (how much) of the force.(how much) of the force.

Net Force Net Force (Unbalanced Force)(Unbalanced Force)

Total force being exerted on an object.Total force being exerted on an object. Ex. Pull a box w/ net force of 5 N, Ex. Pull a box w/ net force of 5 N, A Friend pulls a box w/ net force of 5 NA Friend pulls a box w/ net force of 5 N How much total force is being pulled?How much total force is being pulled?

Net ForceNet Force

If no forces act on an object, the net force on the object is zero.If no forces act on an object, the net force on the object is zero.

Additional Examples- Additional Examples-

http://www.batesville.k12.in.us/physics/phynet/mechanics/newton1/the_net_force.htmlhttp://www.batesville.k12.in.us/physics/phynet/mechanics/newton1/the_net_force.html

Net Force Activity Net Force Activity

Normal ForceNormal Force

The force on an The force on an object that is in object that is in contact with a contact with a surfacesurface– It is perpendicular to It is perpendicular to

the surfacethe surface– It usually is the force It usually is the force

opposite of the opposite of the weight of the object.weight of the object.

EquilibriumEquilibrium

When the net force on something is zero:When the net force on something is zero:That something is in That something is in mechanical equilibriummechanical equilibrium..

What is equilibrium?What is equilibrium?Equilibrium means a state of physical balance.Equilibrium means a state of physical balance.

EquilibriumEquilibrium

Equilibrium Rule: Equilibrium Rule: ∑ ∑ F = 0F = 0

∑ ∑ stands for the “vector sum of”stands for the “vector sum of”

F stands for “forces”F stands for “forces”

EquilibriumEquilibrium

Equilibrium Rule Continued:Equilibrium Rule Continued:The rule says that the forces acting in one direction on The rule says that the forces acting in one direction on an object must be balanced by forces acting in the an object must be balanced by forces acting in the opposite direction.opposite direction.

Example: Forces acting upward must be balanced by forces Example: Forces acting upward must be balanced by forces acting downward.acting downward.

In essence, they must cancel each other out.In essence, they must cancel each other out.

Static EquilibriumStatic Equilibrium

StaticStatic means “not means “not moving.”moving.”

If an object is not moving, If an object is not moving, it is in static equilibriumit is in static equilibrium– This means that the This means that the

weight of the object is weight of the object is canceled out by the canceled out by the normal force.normal force.

Dynamic EquilibriumDynamic Equilibrium

Dynamic Dynamic means means “moving.”“moving.”

An object is in dynamic An object is in dynamic equilibrium when it is equilibrium when it is moving with a constant moving with a constant velocity. velocity. – Example – The force Example – The force

applied to the car is equal applied to the car is equal to the friction acting to the friction acting against it.against it.