MotorsMotorsLesson 9Lesson 9

Thinking About MotorsThinking About Motors What is a motor?What is a motor?

Device that converts energy into mechanical Device that converts energy into mechanical motionmotion

What are motors used for?What are motors used for? Hard drives, disk drives, fans, DVD players etc..Hard drives, disk drives, fans, DVD players etc..

How do motors work?How do motors work?

Magnets- Necessary Component of Magnets- Necessary Component of MotorsMotors

HistoryHistory Named for a region in Asia Minor called MagnesiaNamed for a region in Asia Minor called Magnesia Magnesia was the first location magnetic rocks were Magnesia was the first location magnetic rocks were

found found Earliest Uses- 11Earliest Uses- 11thth Century China Century China

Compass needlesCompass needles Needle is made of a magnet that points towards the Needle is made of a magnet that points towards the

north polenorth pole

How Magnets WorkHow Magnets Work

Magnets AttractMagnets Attract Metals: iron, nickel cobaltMetals: iron, nickel cobalt

Why?Why? Alignment of atomic structure of materialAlignment of atomic structure of material

Magnetic PolesMagnetic Poles

Magnets have two poles Magnets have two poles North pole- attracts south pole, repels northNorth pole- attracts south pole, repels north South pole- attracts north pole, repels southSouth pole- attracts north pole, repels south

Easy way to determine north vs. south poleEasy way to determine north vs. south pole Hold a compass next to a magnetHold a compass next to a magnet The compass needle will point to the south poleThe compass needle will point to the south pole

Mechanical Motion from ElectricityMechanical Motion from Electricity

Hans Christian OerstedHans Christian Oersted Discovered relationship in 1800’s between:Discovered relationship in 1800’s between:

• Mechanical ForceMechanical Force

• MagnetismMagnetism

• ElectricityElectricity

Followed up by Maxwell, Farady and LorentzFollowed up by Maxwell, Farady and Lorentz

Mechanical Motion from ElectricityMechanical Motion from Electricity

Basis for Electric MotorBasis for Electric Motor A wire conducting current will experience a A wire conducting current will experience a

force when it is placed in a magnetic fieldforce when it is placed in a magnetic field

F = iL x BF = iL x B F (Force)F (Force) i (Current)i (Current) L (Length of Conductor)L (Length of Conductor) x (Cross Product)x (Cross Product) B (Magnetic Field Strength)B (Magnetic Field Strength)

Mechanical Motion from ElectricityMechanical Motion from Electricity VectorsVectors

Vectors represent a quantity with a size and Vectors represent a quantity with a size and directiondirection

According to the formula:According to the formula: The force is a cross product of the vectors B The force is a cross product of the vectors B

and iLand iL Cross Product: takes two vectors B and iL and Cross Product: takes two vectors B and iL and

produces a third: BiLsin(produces a third: BiLsin(ӨӨ)) We will only consider vectors at right angles: We will only consider vectors at right angles:

F= iLBF= iLB

Mechanical Motion from ElectricityMechanical Motion from Electricity

Right Hand RuleRight Hand Rule Used to find the direction of the force on the wireUsed to find the direction of the force on the wire Point hand with open palm in direction of first Point hand with open palm in direction of first

vector in the cross product (iL)vector in the cross product (iL) Close fingers in the direction of second vector (B)Close fingers in the direction of second vector (B) Your thumb is now pointing in direction of FYour thumb is now pointing in direction of F

Practice the Right Hand Rule!!!Practice the Right Hand Rule!!!

Inside a MotorInside a Motor Force on current (i) in a magnetic field can be turned Force on current (i) in a magnetic field can be turned

into torque into torque Simple: run current through a loop of wire in a magnetic Simple: run current through a loop of wire in a magnetic

fieldfield Current switches direction based on what side of the loop it Current switches direction based on what side of the loop it

is onis on Results in a pair of forces which cause torqueResults in a pair of forces which cause torque The loop will align with the magnets but will not spin The loop will align with the magnets but will not spin

How Does a Motor Spin?How Does a Motor Spin?

Add physical components to make current change Add physical components to make current change directiondirection Brushes: attached to power source, do not moveBrushes: attached to power source, do not move Commutator: attached to the coil , spins with coilCommutator: attached to the coil , spins with coil

When commutator spins , brushes change direction When commutator spins , brushes change direction which results in current switching directionwhich results in current switching direction

The torque will increase with more coilsThe torque will increase with more coils

A Motor in PiecesA Motor in Pieces