Forces

ForcesChange in motion?What causes an object to start moving, stop moving, or change direction?

UNBANLANCED FORCEWhat is a force?A push or pull

A force is described by strength and directionThe strength of a force is measured in the Newton (N)Arrows are used to represent force:

Combining forcesMost of the time, there are more than 1 force acting on an object at a time

Net force- the combination of all forces acting on an 15 N15 N15 N15 NUnbalanced vs. Balanced ForcesUnbalanced ForcesResult in a net force Can cause a change in the objects motionBalanced ForcesEqual forces acting in opposite directionDo not cause a change in the objects motionThey cancel each other outDraw Force Diagrams in NotebookA book is at rest on a tabletop. Diagram the forces acting on the bookA gymnast is holding on the rings suspended from the ceiling waiting to being.A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant velocity. Consider air resistance.A rightward force is applied to a book in order to move it across a desk at constant velocity. Consider frictional forces. Neglect air resistanceExamples Continued5. A student rests a backpack upon his shoulder. The pack is suspended motionless by one strap from one shoulder.6. A skydiver is descending with a constant velocity. Consider air resistance 7. A force is applied to the right to drag a sled across loosely packed snow with a rightward acceleration 8. A car is coasting to the right and slowing down

FormulaF=maForce = mass x accelerationUnits: Newtons (N)N=(kg)(m/s2)Friction

Force that oppose motion- always in opposite direction of motion

The force that one surface exerts on another when the two surfaces rub against each otherFrictionFriction produces heat! how have you seen this?

The amount of friction depends on:How hard the surfaces push together (force)Types of surfaces involved

SURFACE AREA DOES NOT AFFECT THE AMOUNT OF FRICTIONStatic FrictionActs on an object that are not moving

Strongest- most difficult to overcome

Examples:Desk on the floorParked car on the pavement

Sliding FrictionOccurs when one solid surface slides over another solid surface

Not as strong as static friction

Examples:Bicycle brakesPushing a box along the floor

Rolling FrictionOccurs when an object rolls over a surface

Not as strong as sliding friction

Examples:Shopping cartCar traveling on the road

Fluid FrictionOccurs as an object moves through a fluid

Examples:Surf boarding in the oceanCar as it moves through the air

GravityIs the force that pulls objects toward each other

The law of Universal Gravitation- the force of gravity acts between all objects in the universe!

That means: any two masses exert an attractive force on each otherFactors affecting gravityMass- a measure of the amount of matter in an objectThe more mass an object has, the greater its gravitational force on other objects isDistanceThe farther apart objects are, the lesser the gravitational force between them

The sun has a gravitational force on you..why dont you feel it?The pencil in front of you has a gravitational force on youwhy dont you feel it?

Gravitational AccelerationThe gravitational attraction of Earth causes all falling objects to have an acceleration of 9.8 m/s2

Which direction is Earths gravitational force?WeightWhat is it?The gravitational force exerted on an objectW=m x g g=aCalculate the weight of a truck with a mass of 600 kg. G: m = 600 kgF: W=m x g g = 9.8 m/s/s Find: w = ?W.S.: w = 600kg x 9.8 m/s/s

Answer: 5,880 NMass vs. WeightMass is _________Weight is a FORCE

the more mass an object has, the stronger the gravitational force between the object and Earth. So, the more mass an object has, the more it weighs

Weight can be different if the gravitational force is differentWeightlessnessWhen an object is influences only by the force of gravity, it is said to be in free fall.

Air resistanceAir resistance acts in the opposite direct of an objects motionThe force it opposes is GRAVITY

The amount of air resistance depends on:SpeedSizeShape

Terminal velocity- when the force of air resistance = weight of object no more accelerationWhat happens if you drop 2 objects?What would happen if there was no air resistance?

REMEMBER:ALL OBJECTS IN FREE FALL ACCELERATE AT THE SAME RATE, REGARDLESS OF MASS!!Projectile MotionA projectile is an object that has been projected through the air

A projectile has horizontal and vertical motion

Neglecting air resistance, all falling objects accelerate at the same rate

No matter how fast and object is moving horizontally, the force of gravity acts the same as if it was falling straight down