Transcript Chapter 1
Matter in Motion
A Reference Point is:
an object that appears to stay in place
Motion: an object’s change in position overtime relative to a reference point
Motion can be north, south, east, west, up and down.
Common reference points are: the Earth’s surface, trees, buildings, and sometimes other moving objects
During the interval between the times that these pictures were taken, the hot air balloon changed position relative to a reference point—the mountain.
Speed:
the distance traveled divided by the time interval during which the motion occurred
Example: Time = 10s and Distance=50m Speed
= distance ÷ time = 50m ÷ 10s = 5 m/s
Standard units (SI) for speed is
meters per second (m/s).
Other commonly used units are:
Kilometers per hour (km/hr) Feet per second (ft/s) Miles per hour (mi/h)
Not everything moves at a constant rate though so you need to be able to calculate average speed.
Average Speed =
total distance total time
An athlete swims a distance from one end of a 50 m pool to the other end in a time of 25 s What is the athlete’s average speed?
Step 1: Write the equation for average speed: Average Speed =total distance total time
Step 2: Replace the total distance and total time with the values given, and solve
1.
Kira jogs to a store 72 m away in a time of 36 s. What is Kira’s average speed?
2.
If you travel 7.5 km and walk for 1.5 hr, what is your average speed?
3.
An airplane traveling from San Francisco to Chicago travels 1,260 km in 3.5 hr. What is the airplane’s average speed?
Velocity:
direction the speed of an object in a particular
Is like an object’s rate of change of that objects
position
If speed and direction don’t change then velocity is
constant straight
, so constant velocity is motion along a line
The speeds of these cars may be similar, but the velocities of the cars differ because the cars are going in different directions.
Resultant Velocity:
is a combination of 2 or more velocities
Acceleration:
the rate at which velocity changes over time
An object accelerates if its
speed, direction
or both change Positive acceleration means an
increase
velocity in Negative Acceleration means a
decrease
velocity or what is called deceleration in faster the velocity changes, the greater the acceleration is
Acceleration is measured in
meters per second per second
, or m/s 2
A plane passes over point A a velocity of 240 m/s north. Forty seconds later, it passes over point B at a velocity of 260 m/s north. What is the plane’s average acceleration?
Starting velocity = 240 m/s Final velocity = 260 m/s Time = 40 s Plug in your numbers: 260-240 = 20m/s =
0.5m/s 2 north
40 s 40s
What is the average acceleration of a subway train that speeds up from 9.6 m/s to 12 m/s in 0.8 s on a straight section of track?
An object traveling in a circular motion is always changing its direction so its velocity is always changing, so it’s
accelerating
.
This is called
centripetal acceleration
The blades of these windmills are constantly changing direction. Thus, centripetal acceleration is occurring
Force:
a push or pull exerted on an object in order to change the motion of the object
Force has
size
and
direction
Newton:
the SI unit for force, symbol is N
All forces act on objects Forces do not always cause
motion
Example: you are exerting a force on your chair, however the chair doesn’t move. That is because the floor is exerting a force on the chair You cannot see all forces! For example the air around you is held near Earth’s surface by the force of
gravity
.
Something that you cannot see exerts a force that makes this cat’s fur stand up.
The bulldozer is exerting a force on the pile of soil. But the pile of soil also exerts a force by just sitting on the ground!
Net Force:
the combination of all of the forces acting on an object
When forces are moving in the
same add
them together direction, you When forces are moving in
subtract opposite
direction you the smaller force from the larger one.
When the forces on an object produce a net force of 0N, then those forces are
balanced
Balanced forces do not cause a change in
motion
an object of When the Forces of an object are not 0N, the forces are
unbalanced
and a change in motion occurs.
When forces act in the same direction, you add the forces to determine the net force. The net force will be in the same direction as the individual forces.
When two forces act in opposite directions, you subtract the smaller force from the larger force to determine the net force. The net force will be in the same direction as the larger force.
Because all the forces on this house of cards are balanced, none of the cards move.
The soccer ball moves because the players exert an unbalanced force on the ball each time they kick it
A boy pulls a wagon with a force of 6 N east as another boy pushes it with a force of 4 N east. What is the net force?
A dog pulls on his chew toy with a force of 10 N towards the east. His owner pulls on the other end f the toy with a force of 15 N to the west. What is the net force?
Friction:
a force that opposes motion between two surfaces that are in contact.
Can cause a moving object to
slow down
or eventually
stop
Occurs because the surface of any object is
rough
When the hills and valleys of one surface stick to the hills and valleys of another surface, friction is created
Two factors that affect the amount of friction are: 1) the force
pushing the surfaces together
and 2) the
roughness
of the surfaces.
If the force pushing objects together increases then the
hills and valleys
come in closer contact and the friction increases The
rougher the surface
, the greater the friction is
1.
Kinetic Friction:
friction between moving surfaces
Mount depends on how the surfaces move
Sliding
objects objects experience more friction than
rolling
2.
Static Friction:
to move when a force is applies to an object but does not cause the object
The force of the friction is
balanced
applied with the force Can be overcome with a large enough force
Lubricants
table, etc) : substances applied to reduce friction between objects (motor oil, wax, grease, air on a hockey Switching from sliding to rolling friction (using ball bearings in wheels) Make surfaces that rub together smoother (sanding wood surfaces)
When you work on a bicycle, watch out for the chain! You might get dirty from the grease or oil that keeps the chain moving freely. Without this lubricant, friction between the sections of the chain would quickly wear the chain out.
Make surfaces rougher (sand on ice, textured batting gloves, etc) Increase the force pushing the surfaces together (pressing harder on sandpaper)
No one likes cleaning dirty pans. To get this chore done quickly, press down with the scrubber to increase friction.
http://www.youtube.com/watch?v=efzYblYVUFk&feature=fvwrel
Gravity:
a force of attraction between two objects that is due to their masses
Gravity is a result of
mass
, so matter is affected by gravity Objects experience a pull toward all other objects, called
gravitational force
Because
Earth
has such a large mass, it also has a very large gravitational force, pulling everything toward its center
http://www.youtube.com/watch?NR=1&v=jwPc0kK9VHU&feature=fvwp Proposed the idea of
gravity
He said that
an unbalanced force
on apples caused them to fall from trees, and that an unbalanced force on the moon kept it circling the Earth; and that both of these forces were really the same, a force of attraction called
gravity
Wrote the distance
Law of Universal Gravitation
, which describes the relationships between gravitational force, mass, and
Sir Isaac Newton realized that the same unbalanced force affected the motions of the apple and the moon
Law of Universal Gravitation
: All
objects in the universe attract each other through gravitational force; the size of the force depends on the masses of the objects and the distance between the objects.
http://www.youtube.com/watch?v=Jk5E-CrE1zg
1.
Gravitational Force Increases as
Mass Increases
2.
Gravitational Force Decreases as
Distance Increases
Venus and Earth have approximately the same mass. But because Venus is closer to the sun, the gravitational force between Venus and the sun is greater than the gravitational force between Earth and the sun
The gravitational force between objects decreases as the distance between the objects increases. The length of the arrows indicates the strength of the gravitational force between two objects
Weight:
is a measure of the gravitational force on an object
; SI unit is Newtons (N)
Mass:
is the amount of matter in an object
SI unit is a kilogram (kg) but is also measured in grams (g) or milligrams (mg) ; http://www.youtube.com/watch?v=SegMt7sa42E
The Vomit Comet: http://www.youtube.com/watch?v=BTkFIE_-kL8