Topic: Forces and Motion Aim: Describe Newton’s 3 Laws of Motion. Do Now: Last question on the back of KE and PE reading notes HW: Ditto – How do waves travel through matter? ONLY COMPLETE PART B. CL Waves due Thursday Energy and Waves Exam on Tuesday Decide whether each item below describes kinetic energy or potential energy. 1. An airplane circling in preparation for a landing 2. A pile of coal that will be used for fuel 3. A flag blowing in the wind 4. A hatbox stored on the top shelf of a closet 5. A hammer held above a nail 6. A marble rolling down the aisle of your science classroom 7. A new car battery 8. Glucose stored in plants as a result of photosynthesis 9. An ant crawling across a sandwich at a picnic 10. An eyelash fluttering Calculate the net force in each diagram. State the direction the object will move. 800N – 400N = 400N down 400N 1200N 1200N – 800N = 400N up 800N 800N 2 people are pulling at opposite ends of a rope. The person pulling on the right side of the rope is applying a force of 50N while the person on the left is applying a force of 70N. What will happen to the rope? 1. It will move towards the right. 2. It will move towards the left. 3. It will fall to the ground. 4. It will stay in place. 2 people are pulling at opposite ends of a rope. If they are pulling on the rope with equal but opposite forces, what will happen to the rope? 1. It will stay in place between the 2 people. 2. It will move towards the right. 3. It will move towards the left. 4. It will fall to the ground. Newton • British scientist (1642–1727) • Describe all states of motion (rest, constant motion, acceleration) & how forces cause them Inertia • Tendency of object to stay at rest or in motion unless acted on by an outside force • Greater mass, greater inertia The body is motionless at the start of a race. The athlete must overcome their inertia to start moving! NEWTON’S 1ST LAW OF MOTION • LAW OF INERTIA: An object at rest will stay at rest, OR an object in motion will stay in motion unless acted on by an outside force Air friction is the force that slows the ball & gravity pulls the ball back to Earth. • Example: Soccer ball remains at rest unless acted on by an outside force (kicking) The law of inertia can explain what happens in a car crash. When a car traveling about 50 km/h collides head-on with something solid, the car crumples, slows down, and stops within approximately 0.1s. FIRST LAW: Objects resist a change in motion - an effect you can feel in a starting or stopping car. •Acceleration: how fast velocity (speed) is changing Newton’s 2nd Law: Changing an object’s speed and direction depends on the mass of the object and the amount of force exerted on it. NEWTON’S 2nd LAW • F = mass x acceleration (N) (kg) (m/s2) • Example = A 52kg water skier is being pulled by a speedboat. The force causes him to accelerate at 2 m/s2. Calculate the force that causes this acceleration. –F = ma –F = 52kg x –F = 104.0 N 2 m/s2 1. Identify the difference between the two pictures. 2. Which will have greater acceleration? Support your answer. SECOND LAW: LARGE FORCE GREATER ACCELERATION than a small force. SMALL MASS GREATER ACCELERATION than a large mass. NEWTON’S 3rd LAW • For every action there is an equal and opposite reaction THIRD LAW: Every action has an equal and opposite reaction. If A acts on B, then B acts back on A In a rocket engine, burning fuel produces hot gases. The rocket engine exerts a force on these gases and causes them to escape out the back of the rocket. The gases exert a force on the rocket and push it forward. A swimmer “acts” on the water, the “reaction” of the water pushes the swimmer forward. Whenever one object exerts a force on another object, the other object exerts an equal but opposite force on it. Hammer pushes on stake. Stake pushes on hammer. The hammer acts, the stake re-acts. Let’s summarize… 1. Describe Newton’s 1st law of motion. 2. Identify an example of an outside force that can act on an object. 3. State the equation that makes up Newton’s 2nd law of motion. 4. Describe the relationship between force and acceleration. 5. Describe the relationship between mass and acceleration. 6. Describe Newton’s 3rd law of motion. A driver steps on the gas and the car gradually accelerates to 50km/h. The driver then slams on the brakes to avoid hitting a box on the road. As the car comes to a stop, the driver’s body appears to lurch forward in the seat until restrained by the seat belt. Which law best explains why the driver’s body lurches forward when brakes are suddenly applied? 1. Newton’s 1st Law 2. Newton’s 2nd Law 3. Newton’s 3rd Law 4. The law of gravity The tendency of a stationary object to resist being put into motion is known as 1. acceleration 2. gravity 3. inertia 4. velocity Which of the following wagons should move faster if pushed with the same force? 1. A wagon containing a small boy 2. A wagon containing a small bird 3. A wagon containing a big dog 4. A wagon containing an elephant 1. A chair exerts a force of 20N on the floor. What is the force that the floor exerts on the chair? 1. 10N 2. 20N 3. 21N 4. 40N 2. Which one of Newton’s Law is taking place in the question above? 1. Which of Newton’s three laws of motion is illustrated? 2. State the law of motion that describes the example shown in the diagram. 3. Which of Newton’s laws deals with the acceleration of moving objects?