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Transcript
Name ___________________________________________ Science 9 Date _________________________ FORCES MOTION & ENERGY Chapter 5 Matter & Motion SECTION 1 MEASURING MOTION Motion – an object’s change in position relative to a reference point Speed – the distance traveled divided by the time interval during which the motion occurred (no direction) Average speed = Total distance traveled total time Velocity – Distance and direction traveled over time (has direction) Acceleration – a change in a moving object’s speed or direction Final velocity – starting velocity Acceleration = time it takes to change velocity Negative acceleration = speed decreases Constant speed – no acceleration is occurring SECTION 2 WHAT IS FORCE? Force – a push or pull that always acts on an object Newton – the SI unit for force (symbol, N) Net force – the combination of all of the forces acting on an object 10 N 12 N – 10 N = 2 N to the right 12 N Balanced forces = a net force of 0 (no change in motion) Unbalanced forces – net force is NOT 0 (produce a change in motion – start, stop, or change speed) SECTION 3 FRICTION: A FORCE THAT OPPOSES MOTION Friction – a force that opposes motion between two surfaces that are in contact Kinetic friction – friction between moving surfaces (ex. Brakes on a bike, writing with a pencil, almost all means of transportation – tires moving a car forward) it occurs because of the roughness of any object’s surface Rolling Kinetic Friction – one surface rolls over another surface (easier to move objects on wheels than to slide on the floor) – anything that has wheels bikes, cars , trains Sliding Kinetic Friction – surfaces slide past one another (greater than rolling kinetic friction) ex. Brakes on a bike Static Friction – when force is applied but the object does not move Reduce Friction Lubricants ( motor oil, wax grease) Increase Friction Make surfaces that rub against each other smoother Switch to rolling kinetic friction Make surfaces rougher (sand on icy roads, textured batting gloves) Increase the force pushing the surfaces together SECTION 4 GRAVITY: A FORCE OF ATTRACTION Gravity – a force of attraction between objects that is due to their masses Law of Universal Gravitation – the relationship between gravitational force, mass, and distance. It applies to all objects in the universe Gravitational Force as mass Gravitational Force as Mass Gravitational pull is greater between two objects that have greater masses Weight – a measure of the gravitational force exerted on an object; its value can change with location of the object in the universe Mass – a measure of the amount of matter in an object that does NOT change when location changes Reference point = an object that appears to stay in place that helps you detect motion in another object. BE ABLE TO READ A Time / Distance Graph A Velocity / Time Graph