Download Study Guide - Chapter 5

Chapter 5 Study Guide - Matter in Motion
Motion - an object’s change in position relative to a reference point
1. Reference point - when you watch an object in relation to another object, the object that appears to stay in place
is the reference point.
2. Can be moving or nonmoving
A. nonmoving - the Earth surface, trees, buildings
B. moving – 2 cars on a freeway at different speeds
Speed - the distance traveled divided by the time interval during which the motion occurred.
1. SI unit for speed- meters per second (m/s)
2. Other common units- kilometers per hour (km/h), feet per second (ft/s), miles per hour (mi/h)
Average speed
=
total distance
-------------------total time
Examples: 1. What is your average speed if you take 0.5 h to jog 4000 m?
4000 m  0.5 h = 8,000 m/h
2. If the average speed of a car is 110 km/h, how long will it take the car to travel 715 km?
715 km  110 km/h = 6.5 h
For more practice calculating average speed, complete the 3 practice problems on p. 120 on the test at the top of the page.
See Mr. Tyo for the correct answers.
Velocity - the speed of an object in a given direction
1. Velocity is different than speed; it must include a reference direction
2. An object’s velocity is constant only if its speed and direction do not change. Therefore, constant velocity is
always motion
along a straight line
3. Resultant velocity- when you combine velocities. (Example figure 4, p, 121)
Acceleration - the rate at which velocity changes over time
1. An object accelerates if its speed, direction, or both change
2. An increase in velocity is often called positive acceleration
3. A decrease in velocity is often called a negative acceleration, or deceleration
Average acceleration
=
final velocity - starting velocity
----------------------------------------Time it takes to change velocity
Centripetal acceleration - acceleration that occurs in a circular motion; its velocity is always changing, so it is accelerating
Force - a push or pull exerted on an object in order to change the motion of the object
1. Force has size and direction
2. Just because a force acts on an object doesn’t mean motion will occur
Newton (N) - the SI unit for force
Net Force - the combination of all the forces acting on an object
1. When the forces on an object produce a net force of 0 N, the forces are balanced.
A. Balanced forces do not cause a change in motion
2. When the net force on an object is not 0 N, the forces on the object are unbalanced.
A. Unbalanced forces cause a change in motion
3. Net forces acting in the same direction are added together (example p. 125, figure 3)

25N

+

20N
=

45N
4. When forces are in opposite directions, subtract the smaller force from the larger force
(example p. 126, figure 4)

20N


25N
=

5N (net force)
Friction - a force that opposes motion between two surfaces that are in contact
1. Friction can cause a moving object, such as a ball, to slow down and eventually stop
2. The amount of friction between two surfaces depends on two factors:
A. The amount of force pushing the two surfaces together
B. The roughness of the surfaces (rough surfaces have more microscopic hills and valleys than smooth
surfaces)
3. Friction can be helpful or harmful
There are two types of friction:
1. Kinetic friction - friction between moving surfaces
A. Sliding kinetic friction - surfaces sliding past each other
B. Rolling kinetic friction - using wheels requires a smaller force than sliding friction, used in
transportation
2. Static friction - when a force is applied to an object but does not cause the object to move
A. static friction disappears as soon as the object starts moving and then kinetic friction immediately occurs
Three ways to reduce friction:
1. Lubricants - substances that are applied to surfaces to reduce the friction between surfaces
1. examples: motor oil, wax, grease
2. Switch from sliding to rolling friction, using wheels and ball bearings
3. Make the surfaces rubbing against each other smoother
Two ways to increase friction:
1. Make surfaces rubbing against each other rougher
2. Increase the force pushing the surfaces together
Gravity - the force of attraction between objects that is due to their mass
1. All matter has mass. Gravity is a result of mass. Therefore, all matter is affected by gravity.
2. Earth has a huge mass. Therefore, Earth’s gravitational pull is very large.
Law of Universal Gravitation - all objects in the universe attract each other through gravitational force.
Newton stated that the size of gravitational force depends on two things:
1. Gravitational force increases as mass increases (example: p.136, figure 3)
2. Gravitational force decreases as distance increases (example: p137, figure 5)
-
The gravitational force between you and Earth is large because the Earth has a large mass and the distance is small.
The gravitational force between the sun and the planets is large because the objects have large masses and is strong
even over long distances.
Weight - a measure of the gravitational force exerted on an object.
1. Weight changes depending on where in the universe you are.
2. The SI unit of mass is the Newton
Mass - a measure of the amount of matter in an object.
1. An object’s mass does not change
2. Mass is often measure in grams (g) and milligrams (mg)