Transcript Forces and Motion

Forces
and
Motion
Forces and Motion
Click the picture below to get an introduction to forces and motion!
Position
• Position is the location of an object.
• To describe an object’s position, you say where it is compared with
another object.
• Ex. A tree is ahead of you while running on the playground. As you
run past, the tree is behind you. Your position has changed compared
with the position of the tree.
Reference Point
• A reference point is any object that is not moving
and can be used to describe the position of another
object.
• In the example on the previous slide, the tree is the
reference point.
• Other examples include a desk, a street sign, a line
in the road, etc.
Distance
• After choosing a reference point, you can describe
an object’s position in terms of distance.
• Distance is the length of a line between 2 points.
• Ex. Your chair is 8 cm behind your desk (the
reference point). If you move the chair, its distance
from the reference point changes.
Motion
• Motion (movement) is a
change in position.
When an object is in
motion, its position
changes.
• An object will be in
motion as long as its
position keeps changing
Measuring Motion
• You can use linear measurement tools and a
stopwatch, watch, or clock to measure
motion.
• For example, you might run 100 feet in 10
seconds. That would mean that you can run
10 feet per second.
Describing Motion
• Motion can be described
with words that tell the
direction.
• Direction is the path that
a moving object follows.
• North, South, East, West,
right, left, toward, away
from, etc.
Speed
• Speed is the measure of how far an object
travels in a certain amount of time (how fast
or slowly an object moves).
• Ex. You can ride your bike a distance of 10
kilometers in 1 hour, so your speed is 10 km
per hour.
Speed
• To find an objects speed, you must know how
far an object moved and how long the object
was moving.
• (Speed = Distance ÷ Time)
Graphing Motion
• You can measure the motion of an object by
measuring the distance it travels in a certain
amount of time.
• When you measure those factors, you are
collecting data (pieces of information
including words and numbers).
Data Table
Time (hours)
Distance (miles)
1
50
2
100
3
150
4
200
Distance – Time Graph for Car
250
Distance (miles)
• You can organize the
data you collect with a
data table.
• Once you have
recorded your data on a
data table, a line graph
can be made from that
data. A line graph
shows data as a line on
a grid.
200
150
Car's
Motion
100
50
0
1
2
3
Time (hours)
4
Line Graph
Distance – Time Graph for Car
250
200
150
Car's
Motion
100
50
X-axis
0
1
Y-axis
Distance (miles)
• The period of time that
an object travels goes
along the x-axis
(horizontal).
• The distance traveled by
an object goes along the
y-axis (vertical).
• This is called a distancetime graph.
• If the line on the graph is
straight, the speed of the
object remained
constant.
2
3
4
Time (hours)
Constant Motion and Stopped Motion
• You can look at a distance-time graph and tell what type of motion is
taking place. In the line graphs on the previous slides, constant
motion is taking place, meaning that the car is moving the same
speed the entire time.
• Some distance-time graphs show stopped motion, meaning that the
object was moving, but stopped for some reason.
• Notice that the distance is
increasing as the time
passes until you get to 5
seconds. Time continues
to pass but no distance is
added.
Faster Motion
• The steeper the slope is on the distance-time graph, the
faster the objects speed is. Look at the following graph for
example:
• Notice that the object
moves about 3 meters
per second until the 30
second mark. The object
stops moving for 20
seconds, then begins
moving again at 50
seconds, but at a faster
rate of 15 meters per
second. You can see that
the line has a steeper
slope.
Force and Motion
• Remember that motion is a change in an
object’s position. How do you make things
move?
• To make things move, you apply a force (a push
or a pull).
• When you push an object, you exert a force
away from you. When you pull an object, you
exert a force toward you.
• A force can cause an object to move or change
the way an object moves after it is already
moving. A force can also change the speed of
an object.
• Objects move in the same direction as the force
that acts on it.
Force
of kick
Motion of ball
https://www.brainpop.com/science/motionsforcesandtime/force/
Mass and Motion
• An object’s motion also depends on its mass (the
amount of matter that makes up an object).
• An object’s mass determines how much a force will
change its motion.
• For example, it is harder to push a shopping cart full
of groceries than it is to push an empty shopping
cart.
Gravity
• Gravity is a force that pulls
object toward each other. It can
attract objects toward each
other even if they do not touch.
• Any object with mass exerts a
force of gravity. The more mass
an object has, the greater its pull
of gravity.
• The force of gravity depends on
mass and distance.
https://www.brainpop.com/science/motionsfo
rcesandtime/gravity/
Mass and Gravity
• Objects with more mass
exert a greater force of
gravity.
• For example, think about a
coconut and the Earth. Both
objects pull on each other
because they both have
mass, but Earth’s mass is
much greater, meaning that
its force of gravity is
greater. Earth’s gravity pulls
the coconut down to the
ground.
*
*Disclaimer: Coconuts don’t
actually have faces.
Distance and Gravity
• Distance also determines the force of gravity between two
objects.
• The closer together 2 objects are, the greater the force of
gravity between them.
• The farther apart 2 objects are, the weaker the force of
gravity is between them.
More gravity
Less gravity
Friction
• Friction is a force that acts between surfaces that touch
each other. Friction tends to slow an object’s motion.
• For example if you push a ball across the carpet, friction
between the carpet and ball slows the ball’s motion.
• Different surfaces affect the amount of friction produced.
Rougher surfaces tend to have more friction and smoother
surfaces tend to have less friction.
Air Resistance
• An object can encounter friction as it moves
through the air. This is called air resistance.
• Air resistance acts against the pull of gravity to
slow an objects motion.
Newton’s Laws of Motion
• Click the links below to learn more about Newton’s
Laws of Motion:
– https://www.brainpop.com/science/motionsforcesandti
me/newtonslawsofmotion/
– http://studyjams.scholastic.com/studyjams/jams/scienc
e/forces-and-motion/inertia.htm
– http://studyjams.scholastic.com/studyjams/jams/scienc
e/forces-and-motion/acceleration.htm
– http://studyjams.scholastic.com/studyjams/jams/scienc
e/forces-and-motion/action-and-reaction.htm
Real World Science: Forces
• http://ottosonmiddleschoolteched.weebly.com/real
-world-science---forces-and-newtons-laws.html
Review Videos
• Bill Nye the Science Guy: Motion
Review Games
• http://interactivesites.weebly.com/physicsand-motion.html