Newton’s Laws Learning: • State all 3 of Newton’s Laws • Describe the laws and apply them to different contexts • Use the laws to solve problems Do Now: Complete today’s retrieval grid Keywords: Force Acceleration Resultant Motion Mass Direction Task 1- Newton’s First Law to include: 10 mins! 1. State Newton’s first law. 2. Explain in your own words what your answer to q1 means and 3 examples of when you could observe/use it. Use the keywords ‘balanced, rest, motion, force’ in your answer. 3. Describe the forces acting on a vehicle when: a) It is moving at a steady speed b) It is moving at a changing velocity Use the keywords ‘resultant, vector, scalar, resistive, driving’ in your answers. 4. Define the term inertia and give 2 examples of its importance. Use the keyword ‘tendency’ in your answer. 5. If the resultant force acting on an object is zero, the object could be doing either of 2 things. What are these 2 things? Describe them. Use the keywords ‘remain, velocity, speed, direction, stationary’ in your answer. 6. Describe what is meant by balanced and unbalanced forces and how this links to acceleration. Include at least 2 examples with labels. According to Newton's First Law of motion, an object remains in the same state of motion unless a resultant force acts on it. If the resultant force on an object is zero, this means: • a stationary object stays stationary • a moving object continues to move at the same velocity (at the same speed and in the same direction) Examples of objects with uniform motion Newton's First Law can be used to explain the movement of objects travelling with uniform motion (constant velocity). For example, when a car travels at a constant speed, the driving force from the engine is balanced by resistive forces such as air resistance and friction in the car's moving parts. The resultant force on the car is zero. Newton’s First Law Examples of objects with non uniform motion Other examples of Newton’s first law with non uniform motion include: Other examples of Newton’s first law with uniform motion include: Newton's First Law can also be used to explain the movement of objects travelling with non-uniform motion. This includes situations when the speed, the direction, or both change. For example, when a car accelerates, the driving force from the engine is greater than the resistive forces. The resultant force is not zero. •At the start of their run, a runner experiences less air resistance than their thrust, so they accelerate •A runner at their top speed experiences the same air resistance as their thrust •An object that begins to fall experiences less air resistance than its weight, so it accelerates •An object falling at terminal velocity experiences the same air resistance as its weight The tendency of an object to continue in its current state (at rest or in uniform motion) is called inertia. Task 2- Newton’s Second Law to include: 10 mins! 1. State Newton’s second law (in words). 2. Explain in your own words what your answer to q1 means and 3 examples of when you could observe/use it. Use the keywords ‘unbalanced, acceleration, magnitude, force’ in your answer. 3. F = ma is the equation form of your answer to q1. a) Define each symbol giving its name and unit. b) Describe how to rearrange the equation for m and a. c) Include 2 example calculations with full workings using F=ma. 4. Describe what is meant by the terms proportional and inversely proportional. Apply your answer to F=ma. 5. What is meant by the term ‘inertial mass’? Use the keywords ‘velocity, force, acceleration, ration’ in your answer. 6. Find estimates for the speed, accelerations and forces involved for a family car and lorry travelling at their maximum speeds on a single carriageway. How does this link to Newton’s 2nd law? Newton's Second Law of motion can be described by this equation: The equation F=ma shows that the acceleration of an object is: resultant force = mass × acceleration • proportional to the resultant force on the object • inversely proportional to the mass of the object In other words, the acceleration of an object increases if the resultant force on it increases, and decreases if the mass of the object increases. F=ma force (F) is measured in newtons (N) mass (m) is measured in kilograms (kg) acceleration (a) is measured in metres per second squared (m/s²) Newton’s Second Law Estimations It is important to be able to estimate speeds, accelerations and forces involved in road vehicles. The symbol ~ is used to indicate that a value or answer is an approximate one. The table gives some examples. Example Calculate the force needed to accelerate a 15 kg gazelle at 10 m/s². F=ma F= 15 x10 F = 150N Example Estimate the force needed to accelerate a family car to its top speed on a single carriageway. Using values of ~1,600 kg and ~3 m/s2, and F = ma: 1,600 × 3 = ~4,800 N The ratio of force over acceleration is called inertial mass. Inertial mass is a measure of how difficult it is to change the velocity of an object. Task 3- Newton’s Third Law to include: 10 mins! 1. State Newton’s third law. 2. Explain in your own words what your answer to q1 means and 3 examples of when you could observe/use it. Use the keywords ‘interact, force, equal’ in your answer. 3. Describe and give 3 examples of contact and non contact forces. Which of these links to Newton’s third law? Why? 4. Explain what this symbol means ~ 5. Rockets move forward by expelling gas backward at high velocity. Explain how this is an example of Newton’s 3rd law. Use the keywords ‘thrust, combustion chamber’ in your answer. Include a diagram. • According to Newton's Third Law of motion, whenever two objects interact, they exert equal and opposite forces on each other. • This is often worded as 'every action has Newton’s Third Law Examples of force pairs Newton's Third Law can be applied to examples of equilibrium situation. an equal and opposite reaction'. • However, it is important to remember that the forces act on two different objects at the same time. 1. Pushing a pram There are contact forces between the person and the pram: the person pushes the pram forwards the pram pushes the person backwards 2. Car tyre on a road There are contact forces between the tyre and the road: the tyre pushes the road backwards and; the road pushes the tyre forwards 3. A satellite in Earth orbit There are non-contact gravitational forces between Earth and the satellite: the Earth pulls the satellite and; the satellite pulls the Earth 4. Rockets taking off Rockets move forward by expelling gas backward at high velocity. This means the rocket exerts a large backward force on the gas in the rocket combustion chamber, and the gas therefore exerts a large reaction force forward on the rocket. This reaction force is called thrust. It is a common misconception that rockets propel themselves by pushing on the ground or on the air behind them. They actually work better in a vacuum, where they can more readily expel the exhaust gases. Newton's First Law • An object remains in the same state of motion unless a resultant force acts on it. • Inertia – Higher Tier • The tendency of an object to continue in its current state (at rest or in uniform motion) is called inertia. Newton's Second Law • The acceleration of an object is proportional to the resultant force on the object and inversely proportional to the mass of the object. F= ma Newton's Third Law • Every action has an equal and opposite reaction • AKA: Whenever two objects interact, they exert equal and opposite forces on each other Summary 1. Newton's First Law An object remains in the same state of motion unless a resultant force acts on it. 2. Newton's Second Law F= ma 3. Newton's Third Law Every action has an equal and opposite reaction Plenary Write 1 question (and answer – but keep it hidden) about today’s lesson. Share your Q+As before we leave.
