#### Transcript I. Motion – an objects change in position over time when compared

I. Motion – an objects change in position over time when compared to a reference point. A. Reference point- an object that appears to stay in place; building, trees, etc. Distance and displacement B. Distance- the length that is traveled C. Displacement- the distance between the starting and ending points. D. Speed- the rate at which an object moves; depends on the distance traveled and the time taken to travel that distance. Speed = distance time Calculate speed: • If you walk for 1.5 hours and travel 7.5 km, what is your average speed? • What is your average speed if you take 0.5 hour to walk 4000m? Solving speed using the triangle: Example: If the average speed of a car is 110 km/h, how long will it take the car to travel 715km? E. Velocity-the speed of an object in a particular direction; velocity always includes a direction (N, S, E or W, upward, downward) Velocity = distance / time A direction is always given. • 1. Resultant Velocity – velocity that results when two directions are traveled at once. Ex. A bus travels 15 m/s east. A passenger on the bus walks toward the front of the bus at a speed of 1 m/s. Find the resultant velocity. Example 2: A bus travels 15 m/s while a passenger on the bus moves to the back of the bus at a speed of 1 m/s. Find the resultant velocity. F. Acceleration- the rate at which velocity changes; this can be both positive (speeding up) or negative (slowing down) or simply changing direction. Acceleration = final velocity - initial velocity time Example: A plane passes over Point A with a velocity of 8000 m/s N. Forty seconds later it passes over Point B at a velocity of 10,000 m/s N. What is the plane’s acceleration from A to B? Example 2: A coconut falls from the top of a tree and reaches a velocity of 19.6 m/s when it hits the ground. It takes 2 seconds to reach the ground. What is the coconut’s acceleration? 1.Centripetal acceleration- the acceleration that occurs in circular motion; windmill blades, ferris wheels, roller coasters with loops, jugglers G. Inertia- the tendency of an object to resist change; you keep moving forward after the car stops. The inertia of an object increases as mass increases. H. Momentum- a measure of how hard it is to stop an object; depends on mass and velocity I. Law of Conservation of Momentum- the total momentum of a group of objects remains constant unless outside forces act on the group; friction slows down balls on a pool table II. Force- a push or a pull A. Newton- SI unit of force B. Examples of forcespushing an object, pulling an object, gravity, weight, friction 1. Net force- the force that results from combining all the forces exerted on an object. C. Balanced forces- forces on an object that cause the net force to be zero. Balanced forces do not cause a change in motion or acceleration. (The push is equal to the pull; both sides of the seesaw are equal) D. Unbalanced forces- forces on an object that cause the net force to be other than zero; unbalanced forces produce a change in motion or acceleration. E. Gravity- force of attraction between two objects that is due to their masses and the distance between the objects. (Law of Universal Gravitation) 1. Gravitational force increases as mass increases 2. Gravitational force decreases as distance increases. F. Weight- a measure of the gravitational force exerted on an object. Weight is a force and is measured in newtons. 1. mass- the amount of matter in an object; this remains unchanged no matter how much gravity is exerted on an object. • G. Friction- force that opposes motion between two surfaces that are touching. H. Types of friction: 1. sliding friction- friction that occurs as an object slides across another object; brakes applied on a car, writing with chalk, etc. 2. rolling friction- friction on an object that has wheels in motion 3. fluid friction- friction between water and an object 4. static friction- a force applied to an object but does not cause the object to move I. Reducing friction 1. Lubricants- reduces the friction between them; motor oil, wax and grease 2. Smoother surfaces J. Increasing friction- rougher surfaces (a tire with tread is better for stopping than a bald tire) Newton’s 3 Laws of Motion J. Newton’s 1st Law of Motion- states that an object at rest will remain at rest unless reacted upon by an unbalanced force and an object in motion will remain in motion unless reacted upon by an unbalanced force. • K. Newton’s 2nd law of Motion- states that force = mass X acceleration L. Newton’s 3rd law of Motion- states that for every action force there is an equal and opposite reaction force