Transcript Force and Motion

Motion & Force
~ Review for Unit Test ~
Vocabulary…Know all T-n-T
vocabulary and the following:
Gravity – A force of attraction between objects that is due
to their masses
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 them
Weight – A measure of gravitational force exerted on an
object
Kinetic Friction – Friction between MOVING surfaces
Static Friction – When the force applied doesn’t cause the
object to move
1. To calculate speed, velocity &
acceleration
Speed = Distance/Time -- or D/T
Velocity = D/T plus direction
Acceleration = Change in Velocity (Speed)
Change in Time
V2 – V1
Change in Time
Problem on test for each of these…
Know formulas.
2. Difference between Speed &
Velocity
Speed = D/T
Velocity = D/T plus DIRECTION
3. Difference between mass and
weight
Weight is a measure of gravitational force
on an object…Use weight scales to
measure
Mass is the measure of matter in an object ...
Use balance scales (TBB) to measure
4. How your weight would change if
you were on the moon
The moon has less mass than Earth and
therefore less gravitational force. Your
weight will be less, and approximately 1/6
of your weight on Earth.
5. When is an object’s velocity
constant?
When the object’s speed and/or direction
don’t change.
6. Objects in a circular motion…
Such as a windmill, a Ferris wheel or
Earth’s rotation are always CHANGING
direction, therefore their VELOCITY
changes, and they are ACCELERATING.
7. Graphing Speed
Time on the X axis (horizontal)
Distance on the Y axis (vertical)
8. Graphing Acceleration
Change in time on the X axis
Change in Velocity on the Y axis
9. The difference between constant,
negative and positive acceleration
Constant – Speed or direction doesn’t
change
Negative acceleration – Deceleration…a
decrease in velocity
Positive acceleration – Increase in
acceleration
10. How it is possible to accelerate at
a constant speed
By changing direction, spinning or turning
11. How Net Force is calculated
Forces moving in the same direction (for
example a push to the right and a pull to the
right) are ADDED to determine Net Force
Forces moving in opposite directions (for
example pulling on both sides during tug-ofwar) are SUBTRACTED to determine Net
Force
Problem on the test
12. The difference between balanced
and unbalanced forces
Balanced forces are equal forces acting on an
object and result in a Net Force of Ø Newtons.
There is no motion or no change in motion
when forces are balanced.
Unbalanced forces are not equal and
motion or a change in motion results.
13. Source of Friction
When surfaces are in contact and force is applied
Friction occurs on smooth surfaces -- just less
14. What the amount of friction
depends on
Force pushing the surfaces together and the
amount of roughness of the surfaces
15. The difference between static
friction and kinetic friction
Static Friction – There is no movement when
force is applied.
Kinetic Friction – The friction between moving
surfaces
16. Examples of sliding friction and
rolling friction
Sliding Friction – Book sliding across the table;
Rolling Friction – A pencil rolling across the table.
Anything with wheels rolling on a sidewalk
(Skateboard)
Usually the force of sliding friction is greater
than rolling friction
17. How friction can be harmful or
helpful
Harmful – Erosion of topsoil, worn out engine
parts or overheating engine, machines less
efficient, worn out shoes, holes in socks or
jeans, etc.
Helpful – Traction between the highway and car
wheels, writing with a pencil, walking or
running, to generate heat or energy, etc.
18. Some ways to reduce and
increase friction
To reduce friction – Using sandpaper to smooth a
surface, using oil, wax or grease (lubricants),
switching from sliding to rolling kinetic friction.
To increase friction – Apply greater force or
roughness to the surfaces in contact.
19. The 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 them.
20. How gravitational force changes
when mass increases or distance
increases
When mass increases – Gravitational force
increases
When distance increases – Gravitational
force decreases
Units of Expression
Distance
m, km
Time
s, hr
1.
2.
3.
4.
5.
6.
Speed
m/s; Km/hr
40 seconds
25 km/hr
2 m/s
15 m/s south
5 m/s² north
100 km
Velocity
m/s West
Acceleration
m/s² West
Time
Speed
Speed
Velocity
Acceleration
Distance