7th Grade Science Unit 5 NCFE

Review

Motion Mo#on:  • defined  as  a  change  in  the  posi#on  of  an  object  • results  in  movement  • judged  rela#ve  to  a  reference  point  

Speed • the  distance  an  object  covers  over  #me  • can  be  calculated  using  the  formula:  

speed  =    

distance    ,me  

Reference Point Reference  point:  • defined  as  an  object  or  loca#on  that  is  used  to  determine  if  another  object  is  in  mo#on.  • are  most  o/en  sta#onary  (not  moving).  

Measuring Distance • When we describe motion, we use

units to talk about the distance an object moves. The formula to find distance is Speed X Time.

• When we measure distance, you are measuring the change in location. •  Units: length (meters, yards, miles, etc.)

Acceleration

• Acceleration is a CHANGE in motion • An object is accelerating if it is:

l Speeding up l Slowing down l Changing direction

Calculating Acceleration

• Acceleration is the change in speed per unit of time.

• Acceleration is measured in units of

meters per second per second, or m/s2.

Acceleration = Final speed – Initial Speed Time

Graphing Motion

Steady Motion NO motion

FAST vs. SLOW

FAST

SLOW

Other Motion Graphs

Starting and Stopping •  .

Accelerating/Speeding Up

FORCES A FORCE is a PUSH or PULL in a

particular DIRECTION.

When 2 or more forces act on an object, the forces combine to

form a net force.

Forces may work together ->

Or oppose each other -> <-

FORCES If the forces cancel each other out, and do not cause the object to move, the forces are said to be BALANCED.

If the forces don’t cancel each other out – 1 force is stronger than the

others – the forces are UNBALANCED and will cause a CHANGE IN MOTION.

COMBINING FORCES

Two forces in the same direction can add together to produce a larger net force.

5 N

right

5 N

right

+ =

10 N

right

COMBINING FORCES

Two forces in opposite directions can subtract to produce a smaller net force in the direction of the larger force.

5 N right

10 N left

- =

5 N left

- What is Friction? • Friction is a force that two surfaces

exert on each other when they rub against each other. • The direction of the friction force is

always OPPOSITE to the direction of the motion. • It SLOWS down moving objects!

Friction Force

Direction of Motion

The Force of Gravity • Gravity is the force that pulls all

objects down to the earth.

• Air Resistance helps slow down things that are being pulled by gravity and falling. (It is a form of friction.)

What is WORK?

•  In scientific terms, you do WORK when you exert a FORCE that causes an object to move some DISTANCE in the SAME DIRECTION of the force.

WORK = FORCE x DISTANCE

What 2 things must happen for WORK to be done? • MOTION – The object must move. If the object doesn’t move, there is no work done.

• FORCE & MOTION IN THE SAME DIRECTION • Movement must be in the same

direction as force. If the motion is in a different direction

than the force, there is no work.

What is POWER?

• Power is the rate at which work is being done (or how much work is being done in a unit of time).

• POWER = WORK ÷ TIME • More power means less time to do the

same work OR more work done in the same amount of time. • Power is measured in Watts (W).

Energy is: the ability to do WORK or cause change There are two main kinds of energy… POTENTIAL ENERGY

STORED energy or

Energy that is NOT being used

KINETIC ENERGY

Energy that IS being used or

Energy in MOTION

Examples: Examples:

Review: There are two TYPES of energy: potential and kinetic. Energy can’t be created or destroyed so we need to convert energy we have into what we need. The energy we use comes from many sources: Fossil fuel (coal, oil, natural gas), nuclear power, sun, wind, geothermal, hydropower. Most of this we convert into electricity (electrical energy). There are 6 forms of energy: mechanical, chemical, nuclear, electromagnetic, thermal, electrical . Energy can change from one form into another but is not created or destroyed.

What  are  MACHINES?    

•  Most  people  think  of  complex,  automated,  technical,  or  electronic  gadgets  with  motors…,  but      machines  can  be  much  simpler.    

•  A  machine  is  any  device  that  lets  you  do  WORK  in  an  easier  or  more  effec+ve  way.    

   

How  do  Machines  do  work?  

•  Machines  make  work  easier  by  changing  3  things  about  the  FORCE  you  exert  to  do  work:  v   AMOUNT  of  force  you  exert  v   DISTANCE  over  which  you  exert  force  v   DIRECTION  in  which  you  exert  force  

   

What  are  SIMPLE  MACHINES?  

•  There  are  only  6  basic  kinds  of  simple  machines  that  make  work  easier.  

•  These  6  simple  machines  make  up  all  the  other  compound  machines  we  use  everyday.  

   SIX  SIMPLE  MACHINES  

The  six  simple  machines  are:  •   Inclined  Plane  •   Wedge  •   Screw  •   Lever  •   Wheel  &  Axle  •   Pulley  

What  is  this  electrical  poten#al  called?  

• Sta#c  Electricity  

- - -

- -

- - +

+ + + +

Electricity  that  moves..(Kine#c  electricity)    •  Current:  The  flow  of  electrons  from  one  place  to  another.  

• Measured  in  amperes  (amps)  • How  can  we  control  currents?    With  circuits.  

•  Circuit:  is  a  path  for  the  flow  of  electrons.    We  use  wires.  

There  are  2  types  of  currents:  

• Direct  Current  (DC)  –  Where  electrons  flow  in  the  same  direc#on  in  a  wire.    

• Alterna,ng  Current  (AC)  –  electrons  flow  in  different  direc#ons  in  a  wire  

2  types  of  Circuits:  1)  Series  Circuit  Series Circuit: the components are lined up along one path. If the circuit is broken, all components turn off.

There  are  2  types  of  circuits:    2)  Parallel  Circuit    

• Parallel  Circuit  –  there  are  several  branching  paths  to  the  components.    If  the  circuit  is  broken  at  any  one  branch,  only  the  components  on  that  branch  will  turn  off.  

2  types  of  Circuits:  2)  Parallel  Circuit  

Conductors  vs.  Insulators  

• Conductors  –  material  through  which  electric  current  flows  easily.  

•  Insulators  –  materials  through  which  electric  current  cannot  move.  

What is magnetism?

Magnetism is the properties and interactions of magnets

The earliest magnets were found naturally in the mineral magnetite which is abundant the rock-type lodestone. These magnets were used by the ancient peoples as compasses to guide sailing vessels. Magnets produce magnetic forces and have magnetic field lines

Magnets have two ends or poles, called north and south poles. At the poles of a magnet, the magnetic field lines are closer together.

Unlike poles of magnets attract each other and like poles of magnets repel.

The earth is like a giant magnet! The nickel iron core of the earth gives the earth a magnetic field much like a bar magnet.

What is an electromagnet? When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.