Transcript Unbalanced forces - wvhs.wlwv.k12.or.us

Welcome Scientists!
Today:
Return and Go Over Formative Quiz
Review For Force and Motion Test
Match each of the following:
A. The car is stopped
B. The car is traveling at a constant speed
C. The speed of the car is decreasing
• Graph 1 matches description B because the distance is increasing by the
same amount over time.
• Graph 2 matches description A because the distance is staying the same as
time goes on – this means that its distance isn’t increasing or decreasing – it
is sitting still.
• Graph 3 matches description C because at first, the distance is increasing
with a steep slope and then levels off. This means that the distance isn’t
increasing as fast so it isn’t going as fast.
1. A sailboat travels 100 meters in 50 seconds.
v = d/t
v = 100 m/50 s
v = 2 m/s
2. A dog running through a field if he is covering 23.7
meters in 54 seconds.
v = d/t
v = 23.7 m/54 s
v = 0.44 m/s
3. A bicycle rider travels 50.0 Km in 2.5 hours.
v = d/t
v = 50.0km/2.5 h
v = 20 km/h
•
Answer the following questions and then explain which of Newton’s Laws is being described.
7.
Heavier football players tend to play on the offensive or defensive line. Why?
Because you need more force to change their motion because they have more
mass.
8.
This demonstrates Newton’s Second Law because the force needed to accelerate
them is proportional to their mass - more mass requires more force.
9.
Imagine you are pulling a wagon with a ball in it. You suddenly stop the wagon.
Describe what will happen to the ball at first the ball will be at the back of the wagon.
When you stop the wagon, the ball will roll forward until it hits the front of the
wagon. The ball might bounce out of the front of the wagon if it is going fast
enough.
10. This demonstrates Newton’s First Law because the ball is moving and when you
stop the wagon it will keep moving because you are putting a force on the wagon,
not the ball. Since you are not putting a force on the ball it will continue in
motion because things in motion tend to stay in motion unless acted on by an
unbalanced force.
11. Which of Newton's laws relate acceleration to mass? 2nd
st
12.Which of Newton's laws is also called the law of inertia? 1
13.Which of Newton's laws allows a rocket to accelerate into the
air by burning rocket fuel?
3rd
14.Which of Newton's laws explains what happens when two
skaters push apart on an ice rink?
3rd
15.Which of Newton's laws governs what happens when a
tablecloth is pulled out from under a table full of dishes
without damaging them? 1st
16.Which of Newton's laws is also called the law of
action/reaction?
3rd
• Box 1 will fall and accelerate because the force of
5N down is unbalanced but the forces of 5N to the
right and left balance each other out.
• Box 2 will stay stationary because each force is
balanced by an equal force in the opposite
direction.
• Box 3 will fall and accelerate but not as fast as box 1
because while the forces to the left and right are
balanced there is a net force of 3 N pulling down.
Box 3 won’t accelerate as much as Box 1 because it
is being pulled down with less force.
• Box 4 will accelerate up and to the right because
there are unbalanced forces in those directions
• List and describe at least 3 forces shown in the diagram and
describe the direction in which the force is acting. Explain
clearly.
• For example: The diagram shows the force of…
because…this force is pulling/pushing (direction)
1. The diagram shows an applied force because the girl is
pushing on the pedals of the bike to cause her to move
forward.
2. The diagram shows the force of gravity because we can
assume she is on earth and gravity is always acting on
objects on earth.
3. The diagram shows the normal force because she is on a
surface and is not falling through the planet. This force is
pushing up against gravity.
4. The diagram shows drag and friction pushing against the
motion of the bike because the wheels are in contact with
the road and the bike is colliding with air molecules which
slows it down.
Draw a free-body diagram for the girl
on the bike.
FN
Ff
FA
Fdrag
Fg
Definitions
• Force- a push or a pull
• Balanced forces – forces that are equal and
opposite or when an object has a net force of zero
(all the forces cancel each other out)
• Unbalanced forces – at least one of the forces on an
object is not canceled out
• Net force – any “leftover” unbalanced force on an
object – the sum of all forces on an object Motion –
the change in position of an object
• Free-body diagram – shows all the forces acting on
an object but doesn’t show the environment – only
shows the object as a dot or a square
• Normal force – exists when an object is on a
surface and keeps objects from falling to the center
of the earth. Fn is always perpendicular to the
surface the object is on
• Gravitational force- force of attraction between
any two or more masses
• Applied force – a push or a pull on an object by
another object or living thing
• Friction – a force that opposes motion when the
surfaces of objects are in contact with each other
• Air resistance – a type of friction caused by moving
objects colliding with air molecules
• Acceleration – the change in an objects velocity over
time – how much an object speeds up or slows down
during a period of time
• Average speed – how much an object’s distance or
location changes in a period of time
ave. v = d/t
• Instantaneous speed - actual speed of an object at any
particular moment
• Inertia – the tendency of an object to resist changes in
its motion (more mass means more inertia)
• Newton – unit of measure of force
• Action/Reaction – (3rd Law)
• F=ma – (2nd Law) force is proportional to mass and
acceleration
• Mass - amount of matter in an object