Slide 2 8.1:Forces an object will not change its motion unless a
force is applied Sir Isaac Newton. Force: A push or pull that acts
on any object. Can cause an object to move (kicking a ball) Can
stop a moving object (catching a ball) Can change the motion (ball
bounces off your face) Can change the shape of an object (crushed
cans) Slide 3 8.1:Forces Categories of Forces: Contact Forces only
affect objects they touch (bend, tear, move, stretch, compress or
twist) Are six types: tension, friction, elastic, applied, normal,
air resistance. Slide 4 8.1:Forces Contact Forces: Tension Force
The tension force is the force that is transmitted through a
string, rope, cable or wire when it is pulled tight by forces
acting from opposite ends. Slide 5 8.1:Forces Contact Forces:
Applied Force An applied force is a force that is applied to an
object by a person or another object. If a person is pushing a desk
across the room, then there is an applied force acting upon the
object. The applied force is the force exerted on the desk by the
person. Slide 6 8.1:Forces Contact Forces: Normal Force The normal
force is the support force exerted upon an object that is in
contact with another stable object. For example, if a book is
resting upon a surface, then the surface is exerting an upward
force upon the book in order to support the weight of the book.
Slide 7 8.1:Forces Contact Forces: Friction Force The friction
force is the force exerted by a surface as an object moves across
it. There are at least two types of friction force - sliding and
static friction. Ex. a book slides across the surface of a desk,
then the desk exerts a friction force in the opposite direction of
the books motion. Ex. Brakes Slide 8 8.1:Forces Contact Forces: Air
Resistance Force The air resistance is a type of frictional force
that acts upon objects as they travel through the air. The force of
air resistance is often observed to oppose the motion of an object.
Slide 9 8.1:Forces Contact Forces: Elastic Force (Spring) The
spring force is the force exerted by a compressed or stretched
spring upon any object that is attached to it. An object that
compresses or stretches a spring is always acted upon by a force
that restores the object to its rest or equilibrium position. Slide
10 8.1:Forces Categories of Forces: Action-at-a-Distance Forces are
those types of forces that result even when the two interacting
objects are not in physical contact with each other, yet are able
to exert a push or pull despite their physical separation. Are
three types: gravitational, electrostatic, magnetic Slide 11
8.1:Forces Action-at-a-Distance Forces : Gravity Force The force of
gravity is the force with which the earth, moon, or other massively
large object attracts another object towards itself. By definition,
this is the weight of the object. All objects upon earth experience
a force of gravity that is directed "downward" towards the center
of the earth. Slide 12 8.1:Forces Action-at-a-Distance Forces :
Electrostatic Force (Static Electricity) Is the excess of positive
(+) or negative charges (-) Similar charges repel (push away)
Unlike charges attract (pull together) Slide 13 8.1:Forces
Action-at-a-Distance Forces: Magnetic Force Certain metals have an
electromagnetic field that can either attract (pull) or repel
(push) other metals. Slide 14 8.1:Forces Reading Check Answers, p.
278 1. (a) Action-at-a-distance: gravity 1. (b) Contact: elastic 1.
(c) Contact: friction 1. (d) Action-at-a-distance: electrostatic
Slide 15 Watch Brainpop:Force Slide 16 8.1:Forces Measuring Mass
Mass: the amount of matter in an object (more particles) Is
measured in g, kg Best to use a balance scale to measure Gravity
pulls equally on objects of equal mass Mass stays the same wherever
it is measured Slide 17 8.1: Forces Weight Depends on Gravity
Weight is the amount (measurement) of force on an object due to
gravity Weight changes depending on where it is measured Weight is
technically a force The Newton Force is measured in Newton's (N) 1
Newton = the amount of force needed to hold up an apple against the
force of gravity (approximately) Force = Mass Acceleration Slide 18
Slide 19 8.1:Forces Reading Check Answers, p. 281 1. Newtons 2.
Weight is the amount of force due to gravity on an object. Mass is
the amount of matter in an object. 3. A balance scale 4. Gravity
pulls equally on objects of equal mass, so a balance scale will
work in any gravitational environment. 5. Weight depends on how
much gravity there is. Different gravity means different weight.
Slide 20 8.1: Forces Measuring Force A device called a Force Meter
is used. it uses springs or elastics to that stretch or compress in
response to being pushed or pulled A device called a Force Sensor
is also used It senses pushing or pulling Mass and Weight are
directly proportional: 1 kg = 9.8 N Ex. 50 kg ( 9.8 m/s ) = 490 N
Slide 21 8.1: Forces Forces and Motion Balanced Forces: are equal
forces in opposite directions, Net force = 0 If balanced forces act
on an object that is not moving, it will not move If balanced
forces act on an object that is moving the object will keep moving
in the same (constant) direction and speed Slide 22 8.1: Forces
Forces and Motion Unbalanced Forces: are forces that are not equal
they can cause a change in speed or direction of an object Using
diagrams of arrows to represent different forces is a good idea
Slide 23 Slide 24 8.1:Forces Reading Check Answers, p. 285 1. Force
meters are equipped with a spring or similar elastic device that
stretches or compresses in response to being pulled or pushed. 2.
Friction works against the motion of objects, tending to slow
motion. 3. Balanced forces are equal in strength and oppose each
other in direction. Unbalanced forces are not equal and cause a
change in the speed or direction of an object. 4. Unbalanced forces
can cause an object to begin moving, increase its speed, slow down,
or change direction. Slide 25 8.1: Forces Some Videos:
http://www.bing.com/videos/search?q=unbalanced+f
orce&view=detail&mid=5A230DEC7A1E811BB9B45A23
0DEC7A1E811BB9B4&first=21
http://www.bing.com/videos/search?q=unbalanced+f
orce&view=detail&mid=5A230DEC7A1E811BB9B45A23
0DEC7A1E811BB9B4&first=21
http://www.bing.com/videos/search?q=force+of+moti
on&view=detail&mid=FF4B199810C72857D7E5FF4B19
9810C72857D7E5&first=21
http://www.bing.com/videos/search?q=force+of+moti
on&view=detail&mid=FF4B199810C72857D7E5FF4B19
9810C72857D7E5&first=21 Slide 26 8.1:Forces Check Your
Understanding: # 1 - 7 Slide 27 8.1:Forces Check Your
Understanding: 1. Yes. The goalie caused a change in the motion of
the soccer ball, so there was a force was applied. 2. Basaams mass
would be the same. The force of gravity does not change ones mass.
3. The force of gravity changes from planet to planet. Bathroom
scales rely on gravitational force to pull the user onto the scale;
the greater the pull, the greater the weight reading. The scale
would give an accurate measure of weight for the planet the person
was standing on, but most likely the gravitational force would be
different from Earths so the weight would be different as well. 4.
The force is not a contact force, it is an electrostatic force,
which is an action-at-a-distance force. The balloons do not have to
be in direct contact with the hair in order to exert a force. Slide
28 8.1:Forces Check Your Understanding: 5. (a) Different jumpers
have different masses, so the amount of gravitational force will
vary from person to person. A more massive person will stretch the
bungee cord more when he/she jumps, so the bungee cord must be
carefully adjusted. 5. (b) Yes, it could. The more force applied to
the bungee cord, the more it stretches. A scale next to the bungee
cord that showed the amount of stretch would be an indirect
indicator of force. Slide 29 8.1:Forces Check Your Understanding:
6. There are many different forces in the diagram: Tension force in
the ropes: arrows can be forward or backward or both Friction force
on bottom of box: arrows backward Gravitational force on all items:
arrows downward Elastic force on wagon springs: arrows upward,
downward, or both Electrostatic force between cat hair and comb:
arrows upward, downward, or both Note: There are several other
minor forces present in this diagram: such as the frictional force
between the girls shoes and the ground, the tires and axles, tire
treads and ground, and perhaps even a small amount of wind
resistance. Slide 30 8.1:Forces Check Your Understanding: 7. (a)
The forces are balanced. The diagram should indicate equal and
opposite facing arrows against the car. 7. (b) The sketch should
indicate both arrows facing in the same direction, reflecting the
driver and passenger cooperating to push the car in the same
direction. Forces are unbalanced as the car begins its motion
forward. When the car is moving at steady speed while being pushed,
the force applied by the driver and passenger would be in balance
with the friction force acting against the car. Accept either
correctly explained response. Slide 31 8.2:Pressure Pressure: is
the amount of force that acts on a given area of an object Pressure
is measured with this formula: P = F/A or (P)ressure = (F)orce /
(A)rea Since force is measured in Newton's (N) and area is measured
in square meters (m) then pressure is measured in Newtons per
square meter (N/m) 1 N/m = 1 pascal (Pa) this is very small unit of
pressure 1000 pascal = 1 kilopascal (kPa) - this is commonly used
Slide 32 8.2:Pressure - Questions Oh NoMath! A football player is
tackled by another player and lands with the combined weight of
both players on his knee. If the combined weight of the players is
2400 N and the players knee measures 0.1 m by 0.1 m, how much
pressure is exerted on the turf when the player lands on his knee?
A skateboarder lands on all four wheels after riding a railing. If
the skateboarder has a weight of 900 N and the area on the bottom
of a single wheel is 0.0001 m 2, what pressure does the skateboard
put on the ground? A charity fundraiser fits 12 students into a
small car. If the combined weight of the car and students is 1600
kg and the combined area of the wheels touching the ground is 0.08
m 2, what is the pressure placed on the ground by the car and
students? Slide 33 8.2:Pressure - Answers Answers: P = 2400/0.01
(0.1 x 0.1) = 240,000 Pa or 240 kPa P = 900/0.0004 (0.0001 x 4) =
2,250,000 Pa or 2250 kPa P = 1600/0.08 = 20,000 Pa or 20 kPa Slide
34 8.2:Pressure Review: Volume: is the amount of space taken up by
a substance in a gas particles have lots of space between them gas
has an indefinite volume (determined by surroundings) gas is a
fluid Pressure is the amount of force that acts on a given area of
an object Slide 35 8.2:Pressure Compression: is a decrease in
volume produced by a force Gas can be compressed - because of all
the space between particles This can cause a shape change - because
as pressure increases particles are pushed together As a result the
gas takes up less volume or has been compressed Liquids and solids
are incompressible Slide 36 8.2:Pressure Compressed gas can be used
for doing work example: compressed air; works by taking a large
amount of air and compressing it into a smaller volume Compressed
gas can cause an explosion or an implosion Implosion: heat cause
particles in an open and heated container to move faster and
farther apart. If the container is closed the particles slow and
move closer together. This causes the pressure inside to be less
than pressure outside Explosion: heat cause particles in container
to move faster and farther apart. This causes pressure on the
inside of the container until Slide 37 8.2:Pressure Slide 38
Compression and Deformation: Liquids and solids are incompressible
the particles are already too close together Force is just
transmitted from particle to particle If there are any air pockets
within a solid, it can be deformed Deformation is a change of shape
of a solid without a change of volume (smaller volume) As the air
pockets are compressed the object is deformed Slide 39 8.2:Pressure
- CYU Check Your Understanding p.299 #1 - 6 Slide 40 8.2:Pressure
Reading Check p.296 1. Pressure 2. Compression 3. A gas can easily
be compressed because there is a large amount of space between its
particles. 4. A gas that is trapped in a container and heated will
increase in pressure as the fast-moving particles bounce against
the sides of the container. When the pressure exceeds the ability
of the can to hold it, an explosion will occur. 5. If the pressure
outside of a container is greater than the pressure on the inside,
the walls of the container can be forced inward. 6. Liquids and
solids have very little space between particles, so they cannot be
forced together by ordinary means. Slide 41 8.2:Pressure CYU
Answers 1. As a force is applied, it briefly pushes the particles
of air inside the volleyball closer together. 2. A gas can easily
be compressed because there is a large amount of space between its
particles, but solids and liquids have almost no space between
particles and therefore are very difficult to compress. 3. As the
helium balloon rises, the particles inside the balloon move farther
apart because there is less external pressure on the balloon
forcing the particles together. The expansion of the balloon
increases until the balloon pops. Slide 42 8.2:Pressure CYU Answers
4. (a) The pressure when deep diving is greater due to the weight
of the water. This pressure compresses the air in your ear, which
then applies a force to your eardrum. 4. (b) When you come back to
the surface, the pressure and force on the parts inside your ear
come back to normal. 5. The particles in the can are moving fast
and far apart when heated, forcing particles out of the can. When
cooled, the particles rapidly move closer together. The particles
take up less space and so create an area of low pressure inside the
can. As a result, the relatively high pressure surrounding the can
applies a force to it and crushes it. Slide 43 8.2:Pressure CYU
Answers 6. (a) Football player: P = FA = 950 N (1 m 0.5 m) = 1900
Pa Horse: P = FA = 6000 N (2.5 m 2 m) = 1200 Pa Bricks: P = FA =
8500 N (2 m 2 m) = 2125 Pa 6. (b) Bricks, football player, horse 6.
(c) Pressure also depends on the area over which the force is
applied. In this case, the heaviest object had its weight spread
over a rather large area. Slide 44 8.2:Pressure Watch Bill Nye the
Science Guy: Pressure Slide 45 8.3: Viscosity, Adhesion, and
Cohesion Viscosity: the resistance of a fluid to flow The slower
the flow the greater the viscosity Flow depends on type of
particles: Size of molecules - larger molecules have a harder time
to flow past each other and increase viscosity Shape of molecules
more complicated molecules have a harder time to flow past each
other and increase viscosity Intermolecular forces - attraction
between particles of different charges will cause viscosity to
increase Slide 46 8.3: Viscosity, Adhesion, and Cohesion Thick
liquid greater viscosity, slower flow rate Thin liquid less
viscosity, faster flow rate Viscosity Tests
http://www.youtube.com/watch?v=3KU_skfdZVQ
http://www.youtube.com/watch?v=OKENGIhaf1o&fea ture=related
http://www.youtube.com/watch?v=OKENGIhaf1o&fea ture=related
Slide 47 8.3: Viscosity, Adhesion, and Cohesion Flow Rate: speed at
which a fluid flows from one point to another. Viscosity is
affected by temperature Viscosity affects liquids more than gases
Remember viscosity = resistance to flow Therefore viscosity
increases = less flow Slide 48 Slide 49 Slide 50 Slide 51 Slide 52
8.3: Viscosity, Adhesion, and Cohesion Adhesion: the attraction
between the molecules of two different substances in contact with
each other Adhesion can affect flow Slide 53 8.3: Viscosity,
Adhesion, and Cohesion Cohesion: the strength with which the
particles of an object or fluid attract each other Surface tension
is a type of cohesion Cohesion can affect flow Slide 54 8.3:
Viscosity, Adhesion, and Cohesion Reading Check p.305 1. As flow
rate increases, viscosity decreases. They are inversely
proportional 2. Increasing temperature decreases the viscosity of
liquids. Increasing temperature increases the viscosity of gases 3.
Adhesion is the attraction or joining of two different objects or
fluids to each other. Cohesion refers to the strength with which
the particles of an object or fluid attract each other 4. Fluids
adhere to certain surfaces due to adhesionthe attraction of
different particles to each other. Slide 55 8.3: Viscosity,
Adhesion, and Cohesion Adhesion & Cohesion Vid:
http://www.bing.com/videos/search?q=cohesion+and
+surface+tension&view=detail&mid=82097821DF3D82
CE830E82097821DF3D82CE830E&first=0
http://www.bing.com/videos/search?q=cohesion+and
+surface+tension&view=detail&mid=82097821DF3D82
CE830E82097821DF3D82CE830E&first=0 Adhesion at work:
http://www.bing.com/videos/search?q=liquid+adhesi
on&view=detail&mid=0109BF967D9E29D570D40109B
F967D9E29D570D4&first=0&adlt=strict
http://www.bing.com/videos/search?q=liquid+adhesi
on&view=detail&mid=0109BF967D9E29D570D40109B
F967D9E29D570D4&first=0&adlt=strict Slide 56 8.3:
Viscosity, Adhesion, and Cohesion Check Your Understanding p.309 #1
4, 6 Slide 57 8.3: Viscosity, Adhesion, and Cohesion Check Your
Understanding p.309 1. When pancake syrup is cold, the particles
will be moving slowly, and will be closer together. As a result,
the internal friction of the particles will be greater, increasing
viscosity, and making the flow rate very slow. When the particles
of the pancake syrup gain energy on the hot pancake, they move
faster and farther apart. This decreases the viscosity of the
syrup, and increases the flow rate. 2. The tar has too great a
viscosity when it is cool. Heating the tar reduces the viscosity
and makes it easier to spread. Slide 58 8.3: Viscosity, Adhesion,
and Cohesion Check Your Understanding p.309 3. As the honey cools,
the particles move slower and get closer together. This increases
the viscosity of the honey as it is more difficult for the
particles to flow past one another. 4. The water particles are
attracted to each other due to cohesive forces. This attraction of
water particles to themselves forms a surface tension that can
support objects that are of greater density than the water. 6. (a)
Substance A = 10 cm/s Substance B = 2 cm/s Substance C = 4 cm/s 6.
(b) B (highest), C, A (lowest) Slide 59 8.3: Viscosity, Adhesion,
and Cohesion Chapter Review p. 310 #1, 3-7, 9, 11, 12 Slide 60 8.3:
Viscosity, Adhesion, and Cohesion Chapter Review: 1. The
action-at-a distance forces are magnetic, electrostatic, and
gravitational. Two examples might be hair standing on end after
being combed (electrostatic), and two magnetic checkerboard pieces
repelling each other (magnetic). Students answers may vary 3.(a)
Newtons (N) 3.(b) Pascals (Pa) 4. Tension force is force
experienced by a wire or a rope when it is pulled on at both ends.
Friction force works to slow down or stop motion due to surfaces
rubbing against each other. Slide 61 8.3: Viscosity, Adhesion, and
Cohesion Chapter Review: 5. By sitting on an air mattress, a force
is applied to the air particles inside. This forces the particles
closer together, resulting in compression. 6. The viscosity
decreases, and the molasses flows more easily 7. (a) The forces are
unbalanced because the planes motion is changing. 7. (b) Friction
7. (c) The diagram should show a larger arrow backward
(representing friction) than the arrow forward (representing the
propulsion of the plane). Equal arrows up and down representing the
buoyant force of the water and gravity can also be included in the
diagram. Slide 62 8.3: Viscosity, Adhesion, and Cohesion Chapter
Review: 9. (a) The toe of the shoe is obviously compressing the
soccer ball, and liquids are not compressible by normal means, so
the ball must be filled with a gas. 9. (b) The particles inside the
soccer ball are being compressed. 11. (a) The microwave heats the
marshmallow, adding energy to the particles in the pockets of air.
This makes the particles move faster and farther apart, increasing
the pressure in the small air pockets. The air pockets expand due
to the pressure, making the whole marshmallow expand. Slide 63 8.3:
Viscosity, Adhesion, and Cohesion Chapter Review: 11. (b) When the
marshmallow cools, the particles in the air pockets move slower and
closer together as they lose energy, shrinking the size of the air
pockets and the whole marshmallow. It is likely the expansion of
the air pockets broke many of the air pockets, allowing air to
escape, which shrinks the size of the marshmallow to smaller than
the original size. 12. (a) 5200 Pa 12. (b) 10555.6 Pa 12. (c) 120
Pa
