Download 05 Study Guide

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Science 9
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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