Transcript 10-3 Notes
10-3/10-4 Notes: Newton’s First and Second Laws Newton’s First Law of Motion http://archives.nbclearn.com/portal/site/k12/search (science of NHL Hockey) What is Newton’s First law of motion? It states that an object in motion will stay in motion and an object at rest will stay at rest UNLESS acted upon by an unbalanced force. FYI: The following is copied from the GA Drivers manual. Safety belts are needed because they are the most effective occupant protection in all types of vehicle crashes. • helps you keep control of the vehicle. • helps keep your head from striking the dash or windshield. • helps keep people in the vehicle from hitting each other. • helps spread the crash force across the stronger parts of the body. • helps protect you from injury. • helps keep you from being ejected from the vehicle. What unbalanced forces change an object’s motion on Earth? Gravity and Friction What is the first law called? This law is called INERTIA Do different objects have different inertia? Yes! The inertia of an object depends on it’s mass. How does mass affect inertia? • If an object has more mass, it has more inertia. -- This means the object is harder to start or stop moving. • If an object has less mass, it has less inertia. --- This means the object is easier to start and stop moving. What is Newton’s nd 2 Law? It states that the acceleration of an object depends on the mass of the object and the net force acting upon it. Newton’s Second Law of Motion How is Newton’s 2nd Law Calculated? Force = Mass x Acceleration F=ma What are the units for Force?? The SI unit of force is a Newton which comes from Kg/m/s2 http://www.youtube.com/watch?v=NuyiqITNZKM Example1: The mass is 55 kg and acceleration is 2.0 m/s2 F=ma F = 55 kg x 2.0m/s2 F= 110 kg/m/s2 or 110 N ex2) Acceleration is 3m/s2 and mass is 1,000kg F=ma F= 1000kg x 3m/s 2 F = 3000 kg/m/s 2 F= 3000 N ex3) mass is 25 kg and acceleration is 14 m/s 2 F=ma F= 25kg x 14m/s2 F= 350 kg/m/s 2 F= 350 N How can you increase acceleration? • Decrease the mass in the wagon (take a kid out, pull it the same) • Increase the force applied to the wagon (keep both kids in, pull it harder) What is Newton’s 3rd Law? • It states that if one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. “For every action, there is an equal, but opposite reaction.” Newton’s Third Law of Motion What are the forces called? • The force exerted by the first object is the “action force” • The force exerted by the second object back on the first is the “reaction force” Will action and reaction forces always be equal? • YES Do action and reaction forces cancel out? • NO! The forces are acting on two different objects. What is momentum? • Momentum is a characteristic of moving objects that depends on mass and velocity. How is momentum calculated? • • • • • • • Momentum = Mass x Velocity. Golf ball travels 16m/s and has a mass of 0.045kg A baseball travels at 7m/s and has a mass of 0.14kg A bird travels at 15m/s with a mass of 0.018kg. A car has a mass of 920kg and travels at 25m/s. A dolphin swims at 4m/s and has a mass of 250kg. A manatee has a mass of 350kg and swims at a speed of 2m/s What is the unit momentum is measured in? • Kg-m/s What is the law of conservation of momentum? • Without outside forces, the total momentum is not changed when moving objects interact. How is momentum conserved with two moving objects? • The slower object becomes faster, the faster object becomes slower. How is momentum conserved with one moving object and a stopped object? • The moving object stops, the stopped object moves. How is momentum conserved with connection of objects? • The stopped object and the moving object connect and both move. Workbook Pages 143-146 You do not have to do Target Reading Skills