Simple machines

1. Work & the GRASS method

Lesson 1 

GRASS Method 

What does the GRASS Method Stand for?

• G - Given (what information do you have)

• R - Required (what is the question asking)

• A - Analysis (the formula(s) are you going to use to solve the question)

• S -  Solution – plug the known values (from the given) into the formula (from the analysis) and solve, using units.  Double Check Units

• S - Statement – share the answer in a “therefore” sentence, using units

Work 

• Work - Using force to move an object a distance (when both the force and motion of the object are in the same direction. Work is done when a force is exerted on an object and the object moves a distance. 

  • Joules (J) - Work is measured in Joules. 1 Joule = 1 Newton * meter

  • Work = force applied (newtons) × distance moved (metres) 

  • W = Force x distance W = F x d 

• Energy - The ability to do work.

  • Energy comes from the fuel used in a system. If a human is moving a box, they have to consume food to convert it into cellular energy. 

  • Whereas a machine may use electrical energy to move an object.  

  • The energy is used to apply forces on objects to make the object move. But not all energy is consumed for completing work.

    • Example - When you tried to move a huge rock, you consumed energy, but the rock did not move. Energy was used as your muscles contracted while pushing on the rock. Your heart pumped more blood and your chest muscles moved air in and out of your lungs as you applied more force. In other words, work was done on your internal organs, but not on the rock. 

  • Energy, like work, is measured in joules.

Textbook questions - 2.5 Work - p46-48 - #1-5

2. Forces

Lesson 2

Force 

• Weight (F_g)- How strong gravity (a force) is acting on an object, measured in newtons

  • Equation for Weight (Force) = mass x gravity  

• Mass (g)- The amount of matter in an object

• Force - a push or pull on an object

  • Newtons (N)-  Force, and thus gravity, is measured in newtons

• Main Types 

  • Gravitational - A pull towards the center of an object created by all matter (anything with mass, greater the mass the greater the force)

    •  Earth exerts a force of 9.81 N/kg

  • Electromagnetic - A grouping of different forces that are responsible for movement

    • can be broken down into a few subcomponents 

  • Strong nuclear - the attractions of subatomic particles (like protons and neutrons) 

  • Weak nuclear - the decay of unstable subatomic particles (like radioactive material releasing their charged protons) 

• Everyday forces 

  • Friction - Resistance of motion between two objects that are in contact. When friction occurs, energy is transferred as heat, and to reduce friction, lubrication (usually oil) is added to allow surface to slide with more ease. 

    • Static Friction - keeps objects stationary

    • Sliding Friction - slows moving objects 

  • Normal force - Is the force that surfaces exert to prevent solid objects from passing through it, and is equal to the weight (a force) of an object   

    • Example: The chair you are sitting on has a normal force pushing you up, so you are stationary 

• Drawing Forces 

  • Vector - Vector means it has two key factors

    • Direction - where is the force going (left, right, up, down)

    • Magnitude - the strength of the force, represented by the size of the arrow

      • Larger arrow = greater magnitude (force) 

      • Small arrow = less magnitude (force) 

  • Free-body diagram - is used to create a simple illustration of all forces being applied to an object.  

  • Net Force - Net force is the sum of all the forces, taking into account the magnitude and direction 

Textbook questions - 2.2 Force - p36-39 - #1,3,5

3. Simple Machines Lesson 3

Simple Machines 

*Add Images as needed.

*MA will be applicable for the next lesson

What are Simple machines? - 

DO NOT CHANGE THE AMOUNT OF WORK

As force goes down, distance goes up, and vice versa

examples : 

• Incline plan - A surface that has a sloping end for rising/ lowering

  • Function: Used for moving an object up or down

  • Example: Ramp, slated roads, slide

  • MA - 

• Wedge - A modified inclined plane (two inclined planes back-to-back) that meets at a sharp point. The force changes direction or is magnified to a point.

  • Function: Used to hold, cut or split objects

  • Example: Knives, axes, forks, nails

  • MA - 

• Screw - A modified inclined plane (an inclined plane wrapped around a cylinder, and it converts rotational force to linear force

  • Function: Used to hold or separate or lift objects 

  • Example: Jar lid, light bulb, clamps,  wrenches, spiral staircase  

  • MA - 

• Lever (all 3 classes) 

  • Function: A rigid bar or board that pivots on a fulcrum (a fixed point)

  • Example: Ex. Seesaw, Ex. Wheelbarrow, Ex. Excavator

  • MA - 

• Pulley 

  • Function: Used for lifting heavy objects by changing the direction or amount of force

  • Example:  Flag pole, sailboat, blinds, crane

  • MA - 

• Wheel and Axle 

  • Function: Used for moving or turning things

  • Example: Roller skates, wagons, doorknobs, gears

  • MA - 

Textbook questions - 2.1 Simple Machines - p30-35 - #1& 5 

• #1 - The question is asking what simple machine(s) are seen in a stapler

4. Mechanical Advantage Lesson 4 

Mechanical Advantage 

Update Simple Machines notes to match MA

• Mechanical advantage (MA) - how much easier the simple machine makes completing the work

  • Ideal MA - the ratio of input distance to output distance 

    • The equation for IMA - input distance/output distance

  • Actual MA -the ratio of output force to input force for a given machine

    • The equation for AMA - output force/input force

• Word Analysis 

  • Input force - how much force did you apply to the machine 

  • Output force - how much force did the machine do to the load

  • Input distance - how much did the individual move

  • Output distance - how much did the machine move the load

• Specific notes for Forces on a lever 

  • Effort arm length (EAL) - distance from effort point to fulcrum

  • Load arm length (LAL) - distance from the load to the fulcrum

  • Fulcrum - the point at which the lever moves/balances on

Textbook 2.3 MA. Page 43: 1-4

5. Energy, and Mechanical Efficiency Lesson 5

Mechanical Efficiency 

• Efficiency - 

• Mechanical efficiency - is the comparison (or ratio) of work input to work output

  • The equation for ME #1- output work/input work × 100

  • Actual mechanical advantage/ideal mechanical advantage ×100

Textbook questions - 3.2 Efficiency - p61-63 - #2-3

Textbook questions - 3.3 Work, Energy, and ME - p64-65 - #2,4