Science Unit 2

Systems in Action

Unit 2, Lesson 1

What Is Force?

• Definition:

  • Force is any action that changes the motion of an object.

  • It is described as a push or a pull on an object.

• Classification of Forces:

  1. Contact Forces:

  • Definition: Forces that act on an object by coming into contact with (touching) it.

  • Examples:

    • Hitting a tennis ball

    • Friction

  1. Non-Contact Forces:

  • Definition: Forces that act on an object without physically touching it.

  • Examples:

    • Static electricity

    • Magnetism

    • Gravity

Identification of Forces

• For the following scenarios, classify the forces as either Contact or Non-Contact forces:

  • Contact

  • Contact

  • Contact

  • Non-Contact

  • Non-Contact

Factors Affecting Force

• Force Depends On:

  1. The mass of the object the force is acting on.

  2. The effect of gravity on the object.

• Formula for Force:

  • $\text{Force} = \text{Mass} \times \text{Gravity}$

• Units of Measurement:

  • Force units: Newtons (N)

  • Mass units: Kilograms (kg)

  • Gravity: $9.8 \text{ m/s}^2$

Example Calculation

• Scenario:

  • Jennifer needs to lift a box weighing 25 kg onto a shelf located 2.0 meters above the ground.

• Given Values:

  • Mass = 25 kg

  • Distance = 2.0 m

  • Force = ?

• Calculation Steps:

  • Step 1: Solve for force using the formula:

  • $\text{Force} = \text{mass} \times \text{gravity}$

  • $\text{Force} = 25 \text{ kg} \times 9.8 \text{ m/s}^2$

  • $\text{Force} = 245 \text{ N}$

• Conclusion:

  • Jennifer will exert 245 N of force to lift the box.

  • Remember, $1 \text{ N} = \text{kg} \times \frac{\text{m}}{\text{s}^2}$

Mass Vs Weight

• Definitions:

  • Mass:

  • The amount of matter in an object.

  • Mass remains constant unless the object grows or is broken.

  • Weight:

  • The amount of force acting on an object due to gravity.

  • Weight varies depending on the gravitational pull of the planet you are on.

Activity: Exploring the Relationship Between Mass and Weight

• Instructions:

  1. Record the mass of 5 different objects in grams (g) and kilograms (kg).

  2. Then record the corresponding weight in Newtons (N) in the provided table.

  3. Use the following measurements for the scale:

  • 500 g

  • 1000 g

  • 1500 g

  • 2000 g

  • 2500 g

• Further Tasks:

  • Graph the results.

  • Answer the follow-up questions regarding your findings.

Unit 2, Lesson 2

Systems in Action

Work and Energy

What is Energy?

• Definition: The ability to do work.

• Measurement: Energy is measured in Joules (J).

• Categories of Energy:

  1. Kinetic Energy: Energy due to motion.

  2. Potential Energy: Energy that is stored in an object.

High Potential Energy and High Kinetic Energy

• Reiterates the definitions of kinetic and potential energy:

  1. Kinetic Energy: Energy due to motion.

  2. Potential Energy: Energy that is stored in an object.

What Is Work?

• Definition: Work is the result obtained when a force is exerted on an object and it is moved a certain distance.

• Formula for Work:

  • $Work = Force \cdot Distance$

• Units of Measurement:

  • Work: Joules (J)

  • Force: Newtons (N)

  • Distance: Meters (m)

• Important Note: When calculating work, ensure that the Force and Distance traveled are in the same direction!

Example Problem 2

• Scenario: James uses a force of 90 N to lift a box 1.5 meters upwards.

• Calculation of Work:

  • $Work = Force \cdot Distance$

  • $Work = 90 \text{ N} \cdot 1.5 \text{ m}$

  • $Work = 135 \text{ J}$

• Conclusion: It takes 135 J of work to lift the box 1.5 m.

Example Problem 3

• Scenario: Joanna lifts a box with a mass of 5 kg to a height of 1.2 m.

• Given Data:

  • Mass = 5 kg

  • Distance = 1.2 m

  • Force = ?

  • Work = ?

• Step 1: Calculate Force

  • Formula: $Force = Mass \cdot Gravity$

  • $Force = 5 \text{ kg} \cdot 9.8 \text{ m/s}^2$

  • $Force = 49 \text{ N}$

• Step 2: Calculate Work

  • $Work = Force \cdot Distance$

  • $Work = 49 \text{ N} \cdot 1.2 \text{ m}$

  • $Work = 58.8 \text{ J}$

• Conclusion: It takes 58.8 J of work to lift the box 1.2 m.

Reducing the Force Required to Do Work

• Physics Definition: In physics, "work" is defined as the energy transferred when a force causes an object to move a certain distance.

• Key Concept: If you want to decrease the force while keeping the amount of work constant, then the distance must increase.

• Mathematical Relation:

  • To keep work the same,

  • $Work = Force \cdot Distance$

  • As Force decreases, Distance must increase to maintain the equality.

Unit 2, Lesson 3

Lesson Objectives

• Compare a machine's actual mechanical advantage to its ideal mechanical advantage.

• Explain why the efficiency of a machine is always less than 100%.

• Calculate mechanical advantage and efficiency.

Mechanical Advantage

• Mechanical advantage is the concept that helps in making work easier by reducing the amount of force needed.

• The main focus is on getting the machine to make the job easier for the user without performing more work than necessary.

What are Machines?

• Machines facilitate work by:

  • Increasing the force applied to an object.

  • Increasing the distance over which the force is applied.

  • Changing the direction of the force applied.

Forces to Consider

• When analyzing machines, the following forces are important:

  • Input Force (Fin): This is the force you apply to the machine, such as pushing or pulling.

  • Output Force (Fout): This is the force that the machine applies to the object being worked on, such as lifting a load.

Analyzing Forces in Situations

• It is important to locate and label the input and output forces in different scenarios to better understand machine function and performance.

What is Mechanical Advantage?

• Mechanical Advantage (MA): A measure of how much a machine multiplies the input force or changes its direction. This metric helps quantify how much easier a task becomes when using a machine.

• Actual/Experimental Mechanical Advantage: This is defined as the ratio of output force to input force.

  • Mechanical Advantage (MA): A measure of how much a machine multiplies the input force or changes its direction. This metric helps quantify how much easier a task becomes when using a machine.

  • Actual/Experimental Mechanical Advantage: This is defined as the ratio of output force to input force.

    • Formula: Mechanical Advantage (MA) = Output Force / Input Force

• A machine with an MA greater than 1 indicates that it reduces the effort needed to perform the work.

Example Calculation of Mechanical Advantage

Example 1: Car Jack

• Michael applies a force of 250N to the handle of a car jack, which applies a force of 3000N.

• Calculation of Mechanical Advantage:

  • $MA = \frac{3000N}{250N} = 12$

• This means the car jack provides a mechanical advantage of 12.

Theoretical/Ideal Mechanical Advantage

• Theoretical Mechanical Advantage (TMA): This is defined as the ratio of input distance to output distance.

  • Formula: $TMA = \frac{Input\ distance}{Output\ distance}$

• Example: When using a hammer to remove a nail, if a force is applied to a 30 cm handle and the nail moves 5.0 cm:

• Calculation of Theoretical Mechanical Advantage:

  • $TMA = \frac{30cm}{5.0cm} = 6$

What Does a High Mechanical Advantage Mean?

• A higher mechanical advantage indicates the ability to move heavier objects with less force.

• Machines that have high mechanical advantages require less input force to lift or move an object.

• However, this often correlates with a greater distance over which the force must be applied.

  • Example: A ramp with a high mechanical advantage allows less force to lift an object, but the distance over which the object must be moved is longer.

Comparison of Theoretical and Experimental Mechanical Advantage

• It is important to understand that theoretical mechanical advantage does not always align with experimental mechanical advantage due to real-world inefficiencies.

• Exploring real-life examples helps to illustrate discrepancies between the two measures, such as factors like friction or material properties affecting actual performance in practical situations.

Unit 2, Lesson 4

Systems in Action - Unit 2: Lesson 4

Introduction to Simple Machines

• Simple Machines: A category of machines designed to reduce the force required to accomplish work.

  • Machine Definition: Any mechanical system that assists in performing work by minimizing the effort needed.

Functions of Simple Machines

1. Transmit Forces: Simple machines can transfer forces from one location to another.

2. Change the Direction of the Force: They can alter the direction in which force is applied.

3. Modify the Intensity (Size) of the Force: By using simple machines, the amount of force needed to perform a task can be adjusted.

Levers - A Type of Simple Machine

• Lever Definition: A simple machine characterized by a beam or board that pivots on a fixed point known as the fulcrum.

Components of a Lever

1. Fulcrum: The fixed point around which the lever rotates.

2. Load (Resistance): The object that is being moved by the lever.

3. Effort (Force): The force applied to move the load.

Visualizing the Lever

• Label the Lever: Identify and label the three components (fulcrum, effort, load) on your diagram of the lever.

Classes of Levers

• There are three classes of levers, and the classification is based on the positioning of the fulcrum, the load, and the effort.

First Class Lever

• Definition: The fulcrum is located between the effort and the load.

• Example: See diagram to understand where to place labels for fulcrum, effort, and load on this type of lever.

Second Class Lever

• Definition: The load (or resistance) is situated between the fulcrum and the effort.

• Example: Refer to diagrams for proper labeling of the fulcrum, effort, and load on this lever type.

Third Class Lever

• Definition: The effort (or force) is located between the fulcrum and the load.

• Example: View diagrams for labeling guidance on where to identify each component on this type of lever.

Memory Aid for Lever Classes

• FLE: Helps in remembering the order of components in levers:

  • F = Fulcrum

  • L = Load

  • E = Effort

• The order varies among the three classes of levers.

Mechanical Advantage of Levers

• Mechanical Advantage Defined: The ratio of the effort arm distance to the load arm distance.

  • Effort Arm: Distance from the applied force (effort) to the fulcrum.

  • Load Arm: Distance from the load to the fulcrum.

Calculating Mechanical Advantage

• Example 1:

  • Given: Effort Arm = 20 cm, Load Arm = 40 cm.

  • Mechanical Advantage Calculation: MA = Effort Arm / Load Arm = $\frac{20 cm}{40 cm} = \frac{1}{2}$

  • Result: The lever has a mechanical advantage of ½.

• Example 2:

  • Load Applies: Force = 50 N.

  • Effort Force Used: = 10 N.

  • Mechanical Advantage Calculation: MA = Load Force / Effort Force = $\frac{50 N}{10 N} = 5$

  • Result: The lever provides a mechanical advantage of 5.

Formula

$\text{Mechanical Advantage} = \frac{\text{Load Force}}{\text{Effort Force}} = \frac{\text{Length of Effort Arm}}{\text{Length of Load Arm}}$

Unit 2, Lesson 5

Systems in Action - Pulleys

Introduction to Pulleys

• A pulley is a simple machine that consists of:

  • A wheel

  • A cord or chain

  • The wheel is designed with a groove to hold the cord.

• There are two types of pulleys:

  1. Fixed Pulley

  2. Movable Pulley

Fixed Pulley

• Definition: A fixed pulley is a pulley that is mounted in a location where it does not move during operation.

• Characteristics:

  • Does NOT reduce the amount of force needed to lift an object.

  • Changes the direction of the applied force.

  • Example: If the force is applied downward, the object will move upward.

Diagram Description

• A typical diagram may show:

  • The fixed pulley system with:

  • Force/Effort arrow directed downward.

  • Load arrow directed upward.

Movable Pulley

• Definition: A movable pulley is a pulley that moves with the load it is lifting.

• Characteristics:

  • Reduces the force required to lift an object.

  • Both the load and the pulley move together in the same direction.

Diagram Description

• A typical diagram may show:

  • Movable pulley system with:

  • Load attached to the pulley.

  • Force arrow and load arrow moving upward simultaneously.

Hoist Systems

• Definition: A hoist is a system that combines multiple pulleys.

• Advantages:

  • Dramatically reduces the force required to lift a load.

  • Allows for the load and force to move in opposite directions.

• Key Concept: Combining several pulleys can significantly reduce the effort force needed to lift loads.

Diagram Description

• A typical diagram may illustrate:

  • A hoist system featuring both movable and fixed pulleys.

  • Force and load arrows demonstrating their respective movements.

Types of Pulley Systems – Practice Exercise

• Students are encouraged to identify types of pulleys in the following examples:

  • Single Fixed pulley

  • Single Moveable pulley

  • Double Fixed pulley

  • Double Moveable pulley

  • Triple Fixed pulley

  • Triple Moveable pulley

Mechanical Advantage (MA)

• Definition: Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device, or machine system.

• Calculating Mechanical Advantage: There are three ways to calculate MA:

  Mechanical Advantage (MA)

  • Definition: Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device, or machine system.

  • Calculating Mechanical Advantage: There are three ways to calculate MA:

    1. MA = Number of Supporting Ropes

    • This represents the number of ropes that directly support the load.

    1. $MA = (\frac{\text{Effort (Force) distance moved}}{\text{Load distance moved}})$

    2. Determination Based on Physical Systems:

    • Typically involves analysis of forces and distances in practical applications.

    3. Thrid Fromula

    • $\text{Force} = \text{Mass} \times \text{Gravity}$

  • This represents the number of ropes that directly support the load.

Supporting Ropes and Mechanical Advantage Calculation

• Identifying the Number of Supporting Ropes: This needs to be done in each pulley system to determine mechanical advantage correctly.

• Example of Mechanical Advantage Calculation based on supporting ropes:

  • Supporting ropes = 1, MA = 1

  • Supporting ropes = 2, MA = 2

  • Supporting ropes = 3, MA = 3

  • Supporting ropes = 4, MA = 4

  • Supporting ropes = 6, MA = 6

Practical Exercises

1. Calculate the mechanical advantage of each pulley system given the load force and effort force. This involves identifying highlighted forces and performing the calculation of MA.

2. Force Distribution Analysis: For varying pulley systems, if a force is given for each supporting rope, compare it with load force:

   • Pattern 1: Total load with 1 supporting rope = 100N

   • Pattern 2: Each supporting rope shares load, 50N + 50N = 100N

   • Pattern 3: Each rope = 1/3 of load, etc.

   • This demonstrates how the load force is distributed equally among supporting ropes.

3. Distance Pulled vs. Load Height

   • If each load was lifted 10 cm, calculate how far the rope must be pulled to lift the load.

   • Ratio of distances compared against mechanical advantage:

     • Study how pulling distance thus relates to mechanical advantage derived from supporting ropes.

Ratio Analysis for Mechanical Advantage

• Check your understanding by deriving a third formula for calculating mechanical advantage from the ratio of distances moved in relation to the load height.

• Formulate: Write formulas down based on the exercises performed.

Conclusion

• The study of pulleys encompasses understanding mechanical advantage through various configurations and the distribution of forces.

• Practical applications highlight the significance of effective load management using simple machines such as pulleys.

Unit 2, Lesson 6

Systems in Action - Inclined Plane

Unit Overview

• Focus on the inclined plane as a simple machine and its applications.

• Understanding how tools are used to perform work efficiently.

Inclined Plane Definition

• Also referred to as a ramp, slope, or wedge.

• Purpose: To reduce the force needed to lift a load by increasing the distance over which the work is performed.

Mechanical Advantage (MA)

• Definition: Mechanical Advantage refers to the factor by which a machine increases the force put into it.

• Three Ways to Calculate Mechanical Advantage:

  1. Using Input and Output Distance:

  • $MA = \frac{\text{Input Distance}}{\text{Output Distance}}$

  1. Length of the Inclined Plane (L) and Height of the Inclined Plane (H):

  • $MA = \frac{L}{H}$

  1. Output Force and Input Force:

  • $MA = \frac{\text{Output Force}}{\text{Input Force}}$

• Components Needed for Calculation:

  • Length of plane (L)

  • Height of plane (H)

  • Output Force (F_out)

  • Input Force (F_in)

Practice Problems

Practice 1

• Scenario: An inclined plane 4m long is used to move furniture into a moving truck 1.25m off the ground.

• Given:

  • Length of plane = 4m

  • Height of plane = 1.25m

• Calculate Mechanical Advantage:

  • $MA = \frac{4m}{1.25m} = 3.2$

• Result: The Mechanical Advantage of the inclined plane is 3.2.

Practice 2

• Scenario: It takes 130N to push a 52Kg object up an inclined plane.

• Given:

  • Output force = ?

  • Input force = 130N

  • Mass = 52kg

• Calculate Mechanical Advantage:

  • $MA = \frac{130N}{\text{Output Force}}$

• Result: The mechanical advantage of the inclined plane is 3.92.

Practice 3

• Scenario: Using a ramp to move a heavy box into a moving truck with a known Mechanical Advantage of 2 and ramp length of 2.5m.

• Given:

  • MA = 2

  • Length of ramp = 2.5m

  • Height of ramp = ?

• Calculate the Height of the Ramp:

  • $H = \frac{L}{MA} = \frac{2.5m}{2} = 1.25m$

• Result: The height of the ramp is 1.25m.

Conceptual Understanding

• “Think about it” Section:

  • A screw is conceptually an inclined plane wrapped around a cylinder, showcasing the versatility of the inclined plane in different contexts.

Efficiency of Simple Machines

• Definition: Efficiency quantifies the usefulness of a simple machine and compares the work or energy input to the work or energy output.

• Importance: Most machines are not 100% efficient; energy is often lost as wasted energy.

  • Wasted Energy Examples:

  • Energy loss due to conversion into sound energy.

  • Loss due to thermal energy (heat).

  • Overcoming friction during operation.

Calculating Efficiency

Two Methods to Calculate Efficiency:

1. Work Output vs. Work Input:

   • $\text{Efficiency} = \left(\frac{\text{Work Output}}{\text{Work Input}}\right) \times 100\%$

2. Experimental vs. Theoretical Mechanical Advantage:

   • $\text{Efficiency} = \left(\frac{\text{Experimental MA}}{\text{Theoretical MA}}\right) \times 100\%$

Work Definitions:

• Work Output: The useful work done excluding any wasted energy.

• Work Input: Total work or energy exerted to perform the task.

Example of Efficiency Calculation

• Scenario: Stewart has to put in 7500 J of energy to slide a box up a very rough ramp.

• Given:

  • Work Output: 6750 J (actual work done)

  • Work Input: 7500 J (total energy consumed)

• Calculate Efficiency:

  • $\text{Efficiency} = \left(\frac{6750 J}{7500 J}\right) \times 100\% = 90\%$

• Result: The ramp is 90% efficient, which is considered quite effective for its design and use.

CHAT GPT

🌟 UNIT 2 – SYSTEMS IN ACTION: SUPER-DETAILED NOTES 

2.1 — Measuring Force

⭐ What Is a Force?

A force is a push or a pull that can change the motion of an object.

Force can:

• Start motion
  
  

• Stop motion
  
  

• Speed something up
  
  

• Slow something down
  
  

• Change direction
  
  

Even holding something up requires force (because of gravity).

⭐ Types of Forces

1. Contact Forces

Examples:

• Friction
  
  

• Applied force
  
  

• Normal force
  
  

• Air resistance
  
  

2. Non-Contact Forces

Examples:

• Gravity
  
  

• Magnetism
  
  

• Static electricity
  
  

⭐ How Do We Calculate Force?

Force depends on:

1. Mass
   
   

2. Gravity
   
   

Formula (copy-able):

Force = Mass × Gravity

Gravity on Earth:

g = 9.8 m/s²

Units

• Force → Newtons (N)
  
  

• Mass → kilograms (kg)
  
  

⭐ Example

Jennifer lifts a 25 kg box.

F = 25 × 9.8 = 245 N

⭐ Mass vs. Weight

Mass

• Never changes
  
  

• Measured in kg
  
  

Weight

• Force of gravity on mass
  
  

• Measured in Newtons
  
  

2.2 — Work & Energy

⭐ What is Energy?

Energy = ability to do work
Measured in Joules (J).

⭐ Kinetic Energy

Energy of motion
Examples:

• Running
  
  

• Rolling ball
  
  

• Driving car
  
  

⭐ Potential Energy

Stored energy
Examples:

• Book on shelf
  
  

• Stretched elastic
  
  

• Compressed spring

• When you stretch your hand when you bowl
  
  

⭐ What is Work?

Work happens when a force moves an object in the same direction.

Formula (copy-able):

Work = Force × Distance

Units

• Work → Joules (J)
  
  

• Force → Newtons (N)
  
  

• Distance → meters (m)
  
  

⭐ Example

W = 90 × 1.5 = 135 J

⭐ Making Work Easier

Increase distance → needed force decreases.

2.3 — Mechanical Advantage & Efficiency

⭐ What Are Machines?

Machines help by:

• Multiplying force
  
  

• Increasing distance
  
  

• Changing direction
  
  

⭐ Input vs Output Force

• Input Force (F in) – what you apply
  
  

• Output Force (F out) – what the machine applies
  
  

⭐ Mechanical Advantage (MA)

Actual Mechanical Advantage (AMA):

MA = Output Force ÷ Input Force

Theoretical Mechanical Advantage (TMA):

MA = Input Distance ÷ Output Distance

⭐ Why Actual MA might be smaller than the TMA

Because of:

• Friction
  
  

• Rope stretch
  
  

• Heat
  
  

• Imperfections
  
  

⭐ Efficiency

Formula (copy-able):

Efficiency = (Work Output ÷ Work Input) × 100%

Example:
6750 ÷ 7500 × 100 = 90%

2.4 — Simple Machines & Levers

⭐ Simple Machines

• Lever
  
  

• Pulley
  
  

• Wheel & axle
  
  

• Inclined plane
  
  

• Screw
  
  

• Wedge
  
  

⭐ Lever Basics

A lever has:

• Fulcrum ➞ The point where the lever is supported, the point where it pivots, the point where the lever rests
  
  

• Load ➞ The weight or source of pressure

• Effort ➞
  
  

⭐ 1st Class Lever (E - F - L) (F - L - E ➞ Fulcrum is in the middle)

Fulcrum in middle
Examples:

• Seesaw
  
  

• Scissors
  
  

⭐ 2nd Class Lever (F - L - E) (F - L - E ➞ Load in the middle)

Load in middle
Examples:

• Wheelbarrow
  
  

• Nutcracker
  
  

⭐ 3rd Class Lever (F - E - L) (F - L - E ➞ Effort in the middle)

Effort in middle
Examples:

• Tweezers
  
  

• Fishing rod
  
  

⭐ Mechanical Advantage of Levers

Distance formula:

MA = Effort Arm ÷ Load Arm

Force formula:

MA = Load Force ÷ Effort Force

2.5 — Pulleys

⭐ Types of Pulleys

1. Fixed Pulley

• Changes direction
  
  

• MA = 1
  
  

2. Movable Pulley

• Reduces force
  
  

• MA > 1
  
  

3. Block & Tackle

• Many pulleys
  
  

• Much less force needed
  
  

⭐ Mechanical Advantage of Pulleys

1. Count supporting ropes

MA = number of supporting ropes

2. Force formula

MA = Load Force ÷ Effort Force

3. Distance formula

MA = Effort Distance ÷ Load Distance

Example meaning:
If MA = 3 → pull 3 m of rope to lift load 1 m.

2.6 — Inclined Planes & Efficiency

⭐ Inclined Plane (Ramp)

Reduces force by increasing distance.

Formula:

MA = Length ÷ Height

Or:

MA = Load Force ÷ Effort Force

⭐ Efficiency

Formula (copy-able):

Efficiency = (Work Output ÷ Work Input) × 100%

Example:
6750 ÷ 7500 × 100 = 90%