5 G8 Science Q1- Week 2- Forcessssssssss.ppt

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1. PREPARED BY: TYPE YOUR NAME HERE

2. Infer that when a body
exerts a force on another, an
equal amount of force is
exerted back on it

3. a push or pull acting
on an object
typically measured in
Newtons (kg•m/s
2
)
is a vector

4. •Contact Forces
•Applied
•Normal
•Friction
•Air Resistance
•Tension
•Spring
•Non-Contact
Forces
•Gravity
•Electromagnetic

5. any push or pull on an object created from
another source (person, animal, another object,
etc.)
DOMINO EFFECT

6. the support force exerted on an object
directly related to weight (gravity)
consequence of Newton’s 3
rd
Law
is always perpendicular to the surfaces
in contact
Box
Gravity
Normal
Force
90
0
Box
Gravity
Friction
90
0
N
orm
al
Force

7. exerted by a surface as an object moves
across it or attempts to move across it
opposes the motion of an object
depends on the type of surfaces and the
normal force (weight)
Types
Kinetic
Static
Motion
Friction
In which direction
is the force (friction)
vector pointing?

8. •Friction is the force that opposes
motion between two surfaces that are
touching each other.
•Friction depends on the type of
surfaces that are being pressed
together and the force at which they are
pressed together.
•Example: Friction between your shoes
and the floor is what allows us to walk!
If there was no friction, you would be
constantly slipping and falling!

9. Static friction is friction between two solid objects that are
not moving relative to each other. The static friction force
must be overcome by an applied force before an object can
move.
Rolling friction is the resistive force that slows down the
motion of a rolling ball or wheel. This type of friction is
typically a combination of several friction forces at the
point of contact between the wheel and the ground or
other surface.
Sliding friction is the friction between moving surfaces.
TYPES OF FRICTION

10. NOT MOVING


11. •friction due to air molecules
•acts upon objects as they travel through the
air
•opposes the motion of an object
•most noticeable for objects traveling at fast
speeds

12. force that is transmitted through a string,
rope, cable or wire when it is PULLED tight
by forces acting from opposite ends
directed along the length of the wire and
PULLS equally on the objects on the
opposite ends of the wire

13. force exerted by a compressed or stretched spring
upon any object that is attached to it
for most springs, the magnitude of the force is
directly proportional to the amount of stretch or
compression of the spring
If both springs are the same
size when not compressed, which
spring will apply more force to
the ball when released? Explain
your reasoning.
Images taken from:
http://www.lesjoforsab.com/standard-springs/compression-springs.asp

14. natural force of attraction
between any two objects
factors:
distance – increased distance  less
gravitational pull or vice versa
mass – increased mass  more
gravitational pull or vice versa

15. •force that moving charges exert on one
another
•results from the repulsion of like charges
and the attraction of opposites
-
+
+
+
--
Notice how the
particles with
the same charge
move apart and
the particles
with different
charges move
together.
Compare and contrast gravitational force and
electromagnetic force.

16. visuals that help show net force
use a square and draw all forces acting on the
object.
remember size and direction of vector arrows
are important!
Practice
F
grav
= 5 N
F
fric = 3 N
F
norm
= 5 N
F
app
= 3 N
What do you think the
symbols w/subscripts
represent?
What is the net
force on this object?

17. F
grav = 10 N
F
app
= 20 N F
fric
= 5 N
You throw a baseball to your
friend who is to your left.
Your dog pulls you down the
street on a skateboard in an
eastward direction.
F
grav = 10 N
F
fric
= 5 N
F
norm
= 10 N
F
app
= 15 N

18. F
grav
F
fric
F
grav
F
fric
A skydiver is descending with a
constant velocity. Consider air
resistance.
The same skydiver is
descending after 30 seconds.
Consider air resistance.
What has the skydiver
reached in this scenario?

19. Newton’s 1
st Law
Newton’s 2
nd Law
Newton’s 3
rd
Law

20. •objects at rest remain at rest, and objects
in motion remain in motion with the same
velocity, unless acted upon by an
unbalanced force
•also considered the Law of Inertia
How is this illustrated when riding in a
car? Can you think of other
experiences where this is illustrated?

21. the resistance of an object to a change in
the speed or the direction of its motion
directly related to mass

22. the acceleration of an object increases
with increased force and decreases with
increased mass
the direction in which an object
accelerates is the same as the direction of
the force
Formula: F = ma (or a = F/m)
Shopping Cart Simulation

23. any force that keeps an object moving in a
circle
directed toward the center of the circle
In this case, the force of the
ball as it accelerates around the
circle is pointing inward, toward
the center.

24. 1.What net force is needed to accelerate a 24 kg
dogsled to a rate of 3 m/s
2
?
2. A 1.5 kg object accelerates across a smooth table at
a rate of 0.5 m/s
2
? What is the unbalanced force
applied to it?
F = ma
F = ma
F = =(24 kg)(3 m/s
2
)
72 kg·m/s
2
or 72 N
F =

(1.5 kg)(0.5 m/s
2
)=0.75 kg·m/s
2
or 0.75 N

25. states that every time one object exerts a
force on another object, the second object
exerts a force that is equal in size and
opposite in direction back on the first
object.
How was this illustrated during the
Scooter Games competition? Can you
think of other experiences where this
is illustrated?

26. a quantity that has both direction and magnitude
(size)
drawn as an arrow which shows direction and
magnitude (length of arrow)
consists of two parts: tail and head
Tail
Head
Consider the vectors above. Describe the direction and
relative magnitude (force) of each ball based on the vector.

27. can be combined/added to help determine net force
the overall force acting on an object when all of the
forces acting on it are combined
What is the hockey
puck’s net force?
Applied Force = 25 N
Gravity = 14 N
Friction = 2 N
Normal Force = 14 N
Normal Force = 14 N
Gravity = 14 N
Applied Force = 25 NFriction = 2 N
23 N