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ISAAC NEWTON POSTULATED THREE LAWS OF MOTION

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ISAAC NEWTON POSTULATED THREE LAWS OF MOTION

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1. NEWTON'S FIRST LAW = NEWTON I

2. NEWTON'S SECOND LAW = NEWTON II

3. NEWTON'S THIRD LAW = NEWTON III

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For use in Newton and motion problems.

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Here's the basic idea of each law, but you need to use your CAPS syllabus to state these laws formally.

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An object at rest wants to stay at rest:

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An object in motion wants to stay in motion...

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DEF:
An object continues in a state of rest or uniform velocity (moving at constant speed in a straight line), unless it is acted upon by a net or resultant force

INERTIA DEMOS:

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Can you ID the point where inertia comes into play in each of these snippets in the video?

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ANSWERING QUESTIONS USING NEWTON I, II AND III:

Newton’s first law questions will usually be discussion questions.

Newton’s second law can be asked on its own or it, often, will be asked in conjunction with Newton’s third law.

When setting up equations for a 2-body or 3-body system, an equation for each object is set up separately.

YOU ARE NOT ALLOWED TO TREAT THE TWO OBJECTS AS ONE IN THE SYSTEM.

Solve the equations simultaneously to calculate the unknown quantities.

Remember that tension in a string, cable or even stick (wooden, metal etc.) is constant throughout. It is also noteworthy that the acceleration of all the objects are the same while connected to one another.

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USING INERTIA TO TIGHTEN AN AXE HEAD ONTO HANDLE

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USING INERTIA TO TIGHTEN AN AXE HEAD ONTO HANDLE

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NEWTON 1ST LAW - DISCUSSION ON HOW IT APPLIES 

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NEWTON 1ST LAW - DISCUSSION ON HOW IT APPLIES 

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ALL discussion questions must follow the steps set out below:

EXAMPLE 1:

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EXAMPLE 2:

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Inertia in action: coffee spilling out of mug while walking 

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Inertia in action: coffee spilling out of mug while walking 

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Using Resonant Frequencies to Create an Unspillable Cup

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F net = ma

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350 years old

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NEWTON'S SECOND LAW STATES (in TWO parts!):

When a net force, F net, is applied to an object of mass, m, it accelerates in the direction of the net force.

The acceleration, a, is directly proportional to the net force and inversely proportional to the mass.

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STEMonstrations: Newton's 2nd Law of Motion

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PRAC SET UP:
Determining the relationship between acceleration and mass, and between acceleration and net force actin on an object.

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Use the data to draw graph of acceleration vs. mass of glider:

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STATIC AND KINETIC FRICTION VS NORMAL FORCE GRAPHS

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STATIC AND KINETIC FRICTION VS NORMAL FORCE GRAPHS

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Friction = the force that opposes motion

Friction coefficient = a measure of the "stickiness" of two types of surfaces in contact

The larger the coefficient of friction, the more they will "stick" to each other and therefor will move more difficultly across each other.

If an object is at rest on an inclined plane without slipping, then friction must equal the component of the weight of the object parallel to the incline. This requires greater and greater friction for steeper slopes.

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GREATER STATIC FRICTION ON STEEPER SLOPES FOR OBJECTS AT REST

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GREATER STATIC FRICTION ON STEEPER SLOPES FOR OBJECTS AT REST

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A spring is compressed between two trolleys of different mass as shown in figure 1.20. When the spring is released, it applies a force of 20 N on each trolley (figure 1.21). Assume that the surface is frictionless.

1.1 Calculate the acceleration of the 4 kg trolley.
1.2 Calculate the acceleration of the 2 kg trolley.

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PHET SIMULATION ON FORCES AND ACCELERATION - NEWTON II

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PHET SIMULATION ON FORCES AND ACCELERATION - NEWTON II

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Click on the sim and explore:

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A man applies a horizontal force of 150 N in order to move an 80 kg cupboard across the carpet. A frictional force of 30 N exists between the carpet and the cupboard.

1.1 Draw a free-body diagram of all the forces acting on the cupboard.
1.2 Calculate the acceleration of the cupboard

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Can you identify the action-reaction force pair in this GIF?

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DEF:
When object A exerts a force on object B, object B simultaneously exerts an oppositely directed force of equal magnitude on object A.

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STEMonstrations: Newton's Third Law of Motion

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PHET SIM - explore!

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VERTICAL MOTION AND NEWTON II

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Formula used:
F net = ma

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A person stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads only 0.7 of the person's regular weight.

1. Calculate the acceleration of the elevator.

2. Find the direction of acceleration.

CHOOSE UPWARDS AS POSITIVE.

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DETERMINING NORMAL FORCE AND NET FORCE ON A PERSON IN ELEVATOR.

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Two masses (blocks) are in contact and get pushed by an applied force. Calculate the contact force acting between them as well as the acceleration of the system.

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Two blocks each of mass 8kg are in contact with each other and are accelerated along a frictionless surface by a force of 80N (shown below).
Calculate:

1. The acceleration of the blocks

2. The force which block Q will exert on block P

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Calculate the acceleration of the Atwood machine if the masses are 5kg and 2kg respectively. Assume zero friction.

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AND....LIFT-OFF!

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SPACEX 1ST EVER HUMAN CARGO LAUNCH - MAY 2020🚀

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SPACEX 1ST EVER HUMAN CARGO LAUNCH - MAY 2020🚀

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Two NASA astronauts (Bob and Doug) were launched into space in Elon Musk's CREW DRAGON on 27 May 2020 (during COVID lockdown)

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SpaceX passes final review to launch NASA astronauts on Crew Dragon

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The rest is for HOMEWORK.

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Equilibrium = BALANCED

Forces in equilibrium, are balanced and will act on an object to make it stationary.

Fnet = 0

a = 0

The one force that keeps the other forces in equilibrium, is called the EQUILIBRANT.

EQUILIBRANT = - RESULTANT FORCE

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Triangle law of forces states:
If two forces acting at a point are represented in magnitude and direction by the two adjacent sides of a triangle taken in order, then the closing side of the triangle taken in the reversed order represents the equilibrant of the forces.

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HOW TO GO FROM AN FBD TO A CLOSED TRIANGLE OF FORCES

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HOW TO GO FROM AN FBD TO A CLOSED TRIANGLE OF FORCES

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EXAMPLE: SIGN-POST SUSPENDED BY TWO STRUTS

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EXAMPLE: SIGN-POST SUSPENDED BY TWO STRUTS

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Angle between the two struts = 30°.

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DRAW THE FBD AND TRIANGLE OF FORCES ACTING ON THE SIGN-POST

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DRAW THE FBD AND TRIANGLE OF FORCES ACTING ON THE SIGN-POST

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IF THE SIGN-POST WEIGHT IS 10N, DETERMINE THE FORCE IN THE STRUT AND THE TENSION IN THE ANGLED STRUT RESPECTIVELY.

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IF THE SIGN-POST WEIGHT IS 10N, DETERMINE THE FORCE IN THE STRUT AND THE TENSION IN THE ANGLED STRUT RESPECTIVELY.

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Calculate T1 and T₂:

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PROBLEM 1:
The system below includes 3 blocks of masses m ₁ = 1kg, m ₂ = 2kg and m 3 = 5kg on a frictionless table, linked by massless and frictionless strings and pulleys.
a) Find the magnitude of the acceleration of the 3 blocks.
b) Find the magnitude of the tension of the string between m ₁ and m ₂.
c) Find the magnitude of the tension of the string between m ₂ and m ₃.

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PROBLEM 2:
Three masses are connected on the table as shown below. The table has a coefficient of sliding friction of 0,35. The three masses are 4kg, 1kg, and 2kg, respectively and the pulleys are fricitionless.
(a) Determine the acceleration of the masses.

(b) Determine the tensions in the two cords.

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In the system below, blocks of masses m ₁ =10 kg and m ₂ =30 kg are linked by a massless string through a frictionless pulley. The coefficient of kinetic friction between the inclined plane and mass m ₁ is 0,4.
a) Find the acceleration of the masses.
b) Find the magnitude of the tension in the string.

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a) Calculate the acceleration of the masses.
b) Calculate the tension T.

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TENSION IN STRINGS - EXERCISE 5 IN NOTES - ANSWERS

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TENSION IN STRINGS - EXERCISE 5 IN NOTES - ANSWERS

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EXERCISE - ROCKETS AND LIFTS (ELEVATORS)

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EXERCISE - ROCKETS AND LIFTS (ELEVATORS)

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Calculate the acceleration of the system:

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FREE-BODY DIAGRAMS

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FORCES ON A SKYDIVER REACHING TERMINAL VELOCITY

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Force Example 3 -- terminal speed of skydiver

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Physics teachers. This clip showing runaway truck ramps in action is great for stimulating lots of Forces and Motion discussion 🙂
#chatphysics
#iteachphysics

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Physics teachers. This clip showing runaway truck ramps in action is great for stimulating lots of Forces and Motion discussion 🙂
#chatphysics
#iteachphysics https://t.co/A51vKB0Wx3

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Something went wrong, but don’t fret — let’s give it another shot.

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Physics teachers. This clip showing runaway truck ramps in action is great for stimulating lots of Forces and Motion discussion 🙂#chatphysics#iteachphysics pic.twitter.com/A51vKB0Wx3
— Hookean (@Hookean1) July 3, 2022

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Physics teachers. This clip showing runaway truck ramps in action is great for stimulating lots of Forces and Motion discussion 🙂
#chatphysics
#iteachphysics https://t.co/A51vKB0Wx3

# data[].attributes.attachment_link.metadata.attachment_props.original_text
Physics teachers. This clip showing runaway truck ramps in action is great for stimulating lots of Forces and Motion discussion 🙂
#chatphysics
#iteachphysics https://t.co/A51vKB0Wx3

# data[].attributes.attachment_link.metadata.attachment_props.text
Physics teachers. This clip showing runaway truck ramps in action is great for stimulating lots of Forces and Motion discussion 🙂
#chatphysics
#iteachphysics