Forces and Movement Book pg 23 25, 39-40 Syllabus 1.15-1.18, 1.24
Reflect What is the relationship between mass, force and acceleration?
Learning Outcomes 1. Demonstrate an understanding of the effects of balanced and unbalanced forces on an object. Knew Newton s three laws 2. Demonstrate an understanding that a force produces an acceleration which depends on the resultant force and the mass. 3. Use the equation: F = m x a 4. Use the equation W = m x g 5. Explain the forces acting on an object free falling in air and in a vacuum FORCES DISCOVERY LESSON TASK You need to find out the information for yourself that will help you understand the learning outcomes. After the 2 lessons you should be confident you understand all of these. Below I have listed different tasks you need to complete to help you understand the topic. Balanced and unbalanced forces When more than one force acts on an object, the resultant force will tell us the motion of the object. Watch the video (See below). Write Newton s 1 st Law into your note books. Write a definition for balanced and unbalanced forces into your note books. Then complete worksheet 1. Video: watch the video in lesson 5 on my website cgrahamphysics.com Get the solution sheet from your teacher. Then mark your work using red pen Forces and acceleration You need to understand how acceleration is related to the size of a force. What did your results show you from the experiment last lesson? You need to work out the relationship between force, mass and acceleration and write this in your book, you will need to write 2 statements like this one - e.g. The greater the mass the the acceleration for a fixed force. Also make a note of the formula triangle on page 25 in your textbooks. Use pages 23 25 of the textbook and/or watch the video on my website called Newton s second law of motion to help you. When you are confident about Forces & acceleration complete the WS 2 called Survival forces Terminal Velocity In order to be able to use the formula W = m x g you need to understand what these terms mean. In your books write definitions for Weight (W), mass (m) and gravitational field strength (g). Look into Edpuzzle and watch the movie The difference between mass and weight using epzqr1 You need to understand how the forces acting on a parachutist change during the descent. Use these QR codes to find out more. Think about the force that is always acting downwards, does it change? What is the force that acts upwards, does this one remain constant? Answer the terminal velocity WS 3 Homework: EDPUZZLE Go to www.edpuzzle.com and log in. Join our class using the code epzqr1 You have two short video assignments to complete all associated with this topic. Answer the past paper exam questions TASK: Investigate newton s 3 rd Law. Write a definition into your note book. What are the requirements for a force pair to be a third law pair? Find at least 4 statements. Give two examples with explanations about the third law pairs Finish the multiple choice WS 5 and check your answers. Collect a copy of the incomplete pictures from your teacher WS 4. You need to annotate the pictures with correct force arrows. For each stage add an explanation of what is happening to the motion of the parachutist. Draw and then annotate the graph to explain what each section of the graph is showing
Balanced and unbalanced forces Consider a camel standing on a road. What forces are acting on it? Reaction These two forces would be equal we say that they are BALANCED. The camel doesn t move anywhere. Weight
Balanced and unbalanced forces What would happen if we took the road away? Reaction The camel is acted on by an unbalanced force, which causes it to accelerate. This is called Newton s 1 st law of motion. Weight
Newton s 1 st Law of Motion Basically, a body will remain at rest or continue to move with constant velocity as long as the forces acting on it are balanced. and an unbalanced backwards force will make me slow down An unbalanced forwards force will make me accelerate Newton 1642-1727 Without an unbalanced force, Newton would carry on doing what he was doing. This is called Inertia.
Balanced and unbalanced forces Q. What will these cars do and why?
Balanced and unbalanced forces 1) This animal is either or moving with 2) This animal is getting 3) This animal is getting. 4) This animal is also either or moving with.. Words - Stationary, cgrahamphysics.com faster, slower 2016 or constant speed?
Newton s 2 nd Law of Motion The acceleration of a body is proportional to the resultant force causing its acceleration and is in the same direction. It is inversely proportional to the mass of the object. Newton 1642-1727 In other words force = mass x acceleration F You need to learn this equation!! M A
Force, mass and acceleration 1) A force of 1000N is applied to push a mass of 500kg. How quickly does it accelerate? 2) A force of 3000N acts on a car to make it accelerate by 1.5m/s 2. How heavy is the car? 3) A car accelerates at a rate of 5m/s 2. If it weighs 500kg how much driving force is the engine applying? 4) A force of 10N is applied by a boy while lifting a 20kg mass. How much does it accelerate by? M F A 2m/s 2 2000kg 2500N 0.5m/s 2
Inertial Mass Inertial mass is a measure of how difficult it is to change the velocity of an object: Inertial mass = force / acceleration Determine the initial mass of the following: 1) A car that needs a force of 2000N to accelerate it by 1m/s 2. 2) A bus that accelerates at a rate of 0.5m/s 2 when 5 people push it, each with a force of 750N. Newton 1642-1727 2000kg 7500kg
Weight vs. Mass Earth s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N. Weight = Mass x Gravitational Field Strength (in N) (in kg) (in N/kg) W You need to learn this equation!! M g 1) What is the weight on Earth of a book with mass 2kg? 2) What is the weight on Earth of an apple with mass 100g? 3) Charles weighs 700N on the Earth. What is his mass? 20N 1N 70kg 4) On the moon the gravitational field strength is 1.6N/kg. What will Charles weigh if he stands on the moon? 112N
More information about Weight 1) How much does 1kg weigh on the Earth? 2) How much does 2kg weigh? 3) How much does 3kg weigh? 4) What are you noticing about your answers? Whatever mass goes up by, weight goes up by the same ratio. For example, if you double mass you double weight. This is called proportionality : Weight ~ Mass
Acceleration due to Gravity If I throw this ball upwards with a speed of 40m/s why does it come back down again? The ball is acted on by a force called gravity, which accelerates the ball downwards at a rate of 10m/s 2 near the Earth s surface. Extension question how far up would the ball go? 1) Take u = 40m/s and v = 0m/s (at the top of the throw) 2) Take a = 10m/s 2 3) Therefore s = 80m
Terminal Velocity Consider a ball falling through a liquid: Some questions to consider: 1) What forces are acting on the ball? 2) How do those forces change when the ball gets faster? 3) Will the ball keep getting faster? Explain your answer in terms of forces
Terminal Velocity Consider a skydiver: 1) At the start of his jump the air resistance is so he downwards. 2) As his speed increases his air resistance will 3) Eventually the air resistance will be big enough to the skydiver s weight. At this point the forces are balanced so his speed becomes - this is called TERMINAL VELOCITY Words increase, small, constant, balance, accelerates
Terminal Velocity Consider a skydiver: 4) When he opens his parachute the air resistance suddenly, causing him to start. 5) Because he is slowing down his air resistance will again until it balances his. The skydiver has now reached a new, lower. Words slowing down, decrease, increases, terminal velocity, weight
Velocity-time graph for terminal velocity Velocity Speed increases Parachute opens diver slows down Terminal velocity reached New, lower terminal velocity reached Time Diver hits the ground
Newton s Third Law of Motion When an object exerts a force on another object the second object will push back just as hard Newton s Cradle
Newton s third law. Every action force had a equal reaction force in the opposite direction. Alternatively: All forces come in pairs, you can t apply a force without receiving the same force back. Requirements to be a third law pair: Same type of force Same line of action Equal and opposite Must act on two different objects
Cycling Running Skateboarding A car A plane flying. Examples Pick one of the above activities and explain how the forces involved follow Newton s three laws.