Newton's Three Laws of Motion
Everything in the Universe is in motion all the time. You may think that you are sitting in chair, stationary, but in fact, you are moving through space at 1300 km/h as the Earth spins on its axis. The entire Solar System is orbiting around the center of the Milky Way galaxy at an amazing speed of 828,000 km/h. On a much smaller scale, molecules are whizzing around in the air and electrons are orbiting inside them. Understanding motion is one of the keys to understanding the world around us. Newton developed his three laws of motion in 1678 and they are still used today - from calculating your ETA on your navman, to finally measuring the achievable speed of a cheetah just last year, to determining the launch trajectory of the space shuttle.
Let's Build a picture of Newton's Laws of Motion
Watch this youtube video to begin your understanding of Newton's Laws of Motion. Write down an explanation of each law |
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Reference: CS5 9.4) Inertia - Newton's First Law
An object at rest will remain at rest OR an object travelling at constant speed will remain at constant speed
UNLESS acted upon by an UNBALANCED force.
Balanced Forces - these objects will remain at rest
Let's draw diagrams of:
a) People in a car that is going around a corner b) People in a car that suddenly stops. These people DO NOT have a seat belt on c) People in a car that suddenly stops. These people DO have a seat belt on Here is a clickview video on "Balanced and Unbalanced Forces" if you need more clarification |
Questions to Think About:
Q1: State whether the following statements are true or false: a) An object needs a force to start moving b) Passengers are thrown forward in a head-on collision c) A typical accident takes one to two seconds d) You have enough time in a collision to brace yourself to avoid injury e) To keep something moving on the Earth, you need to keep pushing Q2: Explain using Newton’s first law what happens to a car that approaches a curve on an icy highway too fast. Q3: Explain using Newton’s first law what happens to people in a car that suddenly comes to a stop. Q4: A thread supports a mass hung from the ceiling as shown in the diagram to the left. All threads have the same strength and thickness. Which thread will break (and why) if the bottom thread is pulled a) Quickly b) Slowly Extension Questions - CS5 Section 9.4) Inertia and Newton's First Law Activities Q 1 - 8 |
Inertia Inertia is the tendency of an object to resist changes to its motion. The heavier an object is, the greater its inertia. For example it is harder to stop a truck moving at 60 km/h than it is to stop a small car moving at 60 km/h The more speed an object has, the greater its inertia. For example it is harder to stop a car moving at 100 km/h than if it is moving at 20 km/h We experience inertia everyday. Here are some everyday examples: 1) When the bus stops, we continue to move forward due to our inertia AND Newton's first law. We are resisting the change to our motion and trying to keep going forwards rather than stop. 2) When the bus accelerates, we fall backwards due to our inertia AND Newton's first law. We are resisting the change to our motion and trying to remain stationary. 3) When your car turns left, your body appears to move to the right. In actual fact, your body is trying to continue moving forward ie resisting change in your motion 3) Tablecloth trick - watch the video provided or try it at home yourself with an object that is around 700g - 1kg on a piece of A4 cardboard 4) Watch this clickview video "Inertia and Newton's First Law" and make any suitable notes to improve your understanding of inertia 5) Extension Work - Watch this clickview video "Types of Inertia" and make notes in your exercise book |
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Reference: CS5 section 9.5) Acceleration and Newton's Second Law
Newton's Second Law of Motion is still used today to determine the acceleration and amount of fuel required for many different vehicles such as cars, aeroplanes and the space shuttle!!!
There are two forces acting on the space shuttle as it blasts off:
a = F/m = 7,000,000 / 2,200,000 = 3.2 m/s2 In other words, the space shuttle is gaining speed at the rate of only 3.2 m/s (or 11.5 km/h) each second. No wonder the blast-off seems to take forever! Newton's second law also explains why the small acceleration at blast-off is not a problem. As the fuel is rapidly burnt, the mass of the space shuttle gets smaller. As this happens, the acceleration gradually increases, and the space shuttle gains speed more quickly. Remember that for a given net force, the less the mass, the greater the acceleration. 1) Complete Q1 of worksheet 6.4) Calculating Force 2) Complete Force versus Acceleration Graphs Worksheet - answers 3) Answers to worksheet 9.3) Newton's Second Law 4) Velocity versus time graph worksheet and Answers |
Newton's Third Law of Motion - Action/Reaction
Reference: CS5 Section 9.6) Forces in Pairs - Newton's Third Law For every Action force, there is an EQUAL and OPPOSITE Reaction Force. This means that forces come in pairs. For example think about what is happening as you sit on your chair. You are exerting a downward force on the chair. This is the action force. The chair exerts an equal and opposite ie upward force on you. This is the reaction force. Otherwise the chair would collapse and you would fall on the floor! Rockets are based on balloon technology and Newton's Third Law. Demo: Balloons and Newton's Third Law Prac: Make a staged rocket using balloons |
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A balloon provides a simple example of how a rocket engine works.
* What is happening? - The balloon contracts when you let it go and the air trapped inside the balloon is pushed out the open end, causing the balloon to move forward. * Why? 1) The force of the balloon pushing the air out is the "action force". 2) The "reaction force" as predicted by Newton's Third Law of Motion is the force of the air pushing back on the balloon which causes the balloon to move forwards. |
1) Newton's Second Law