How do you know if something is in motion? Motion – changing position in space

How do you know if something is in motion?


Motion – changing position in space.



Reference Point – an object that is considered stationary



Reference Point – an object that is considered stationary (not moving).

The Earth is moving, so everything on Earth is in motion.


Two ways the Earth moves are:

1. Rotation



1. Rotation (spinning)



1. Rotation (spinning) – this causes day and night.




2. Revolution




2. Revolution (going around the Sun) -




2. Revolution (going around the Sun) – this causes the seasons to change.



Reference Point – an object that is considered stationary (not moving). We compare moving objects to a reference point so that we can make measurements of its motion:




TIME




TIME

DISTANCE




TIME

DISTANCE

SPEED




TIME

DISTANCE

SPEED (velocity) – how fast an object is moving




TIME

DISTANCE


Speed formula

ds t




TIME

DISTANCE


E.g. If you fly 660 Km in 60 minutes, what is your speed?

ds t




TIME

DISTANCE


E.g. If you fly 660 Km in 60 minutes, what is your speed?

2) If you travel 40 Km/h for 5 hours, how far will you go?

ds t

Acceleration -

Acceleration – changing something about your motion:

Acceleration – changing something about your motion: 1. speeding up


2. slowing down


2. slowing down 3. changing direction


2. slowing down are all ways to accelerate 3. changing direction



Constant speed -



Constant speed – keeping the same speed all the time.



Constant speed – keeping the same speed all the time. A graph showing constant speed would have

T i m e

Distance



Constant speed – keeping the same speed all the time. A graph showing constant speed would have a straight line.

T i m e

Distance

Time (seconds)

Dis

tan

ce (

mete

rs)

00

2 4 6 8

10

20

30

10

40

50

60

70

80

12 14 16 18 20 22 24

3 People Running a Course

BobRayGreg

T i m e

Distance

Varying the speed will give a curve with different slopes.

T i m e

Distance


faster

faster

T i m e

Distance


slower

faster

slower

faster

Acceleration has a formula too:

Acceleration has a formula too (when speed changes):

S

a t

S = change in speed


S

a t

S = change in speedS = S2 – S1)


S

a t


a = rate of acceleration


S

a t



t = time


S

a t



t = time

A positive acceleration means that the object is getting faster;


S

a t



t = time

A positive acceleration means that the object is getting faster; a negative acceleration means slowing down.

A car going 80 m/s speeds up to 100 m/s in 4 seconds. What is its rate of acceleration?

S

a t


S

a t


S1 S

a t


S1

S2

S

a t


S1

S2time

S

a t


S1

S2time

S = S2 – S1S

a t


S1

S2time

S = S2 – S1 = 100 – 80 = 20 m/s S

a t


S1

S2time

S = S2 – S1 = 100 – 80 = 20 m/s

a =S

t

S

a t


S1

S2time

S = S2 – S1 = 100 – 80 = 20 m/s

a =S

t204

=

S

a t


S1

S2time

S = S2 – S1 = 100 – 80 = 20 m/s

a =S

t204

= = 5 m/s2

S

a t

A car going 80 m/s slows down to 20 m/s in 5 seconds. What is its rate of acceleration?

S

a t


S

a t


S1 S

a t


S1

S2

S

a t


S1

S2time S

a t


S1

S2time

S = S2 – S1 =

S

a t


S1

S2time

S = S2 – S1 = 20 – 80 =

S

a t


S1

S2time

S = S2 – S1 = 20 – 80 = - 60 m/s

S

a t


S1

S2time

S = S2 – S1 = 20 – 80 = - 60 m/s

a =

S

t

S

a t


S1

S2time

S = S2 – S1 = 20 – 80 = - 60 m/s

a =

S

t=

- 60 m/s

5 sec.

S

a t


S1

S2time

S = S2 – S1 = 20 – 80 = - 60 m/s

a =

S

t=

- 60 m/s

5 sec.= -12 m/s2

S

a t

Solve for the new speed:

1. A stopped car accelerates at a rate of 4 m/s2. What is its new speed after 6 seconds?

S

a t


2. A train going at a speed of 30 m/s starts to accelerate at a rate of 2 m/s2. What is its new speed after 12 seconds?

S

a t


3. A train going at a speed of 30 m/s starts to accelerate at a rate of -2 m/s2. What is its new speed after 10 seconds?

S

a t


4. A car going at a speed of 40 m/s starts to accelerate at a rate of 3 m/s2. What is its new speed after 5 seconds?

S

a t


5. A motorcycle is going at a speed of 50 m/s. The bridge ahead is out. If it starts to accelerate at a rate of -12 m/s2 for 4 seconds it has left before going off the bridge, will he stop in time?

S

a t

Galileo

Galileo found that all objects should fall at the ____ rate.

Galileo found that all objects should fall at the same rate.

Galileo studied falling objects and discovered that all things fall at the same rate, despite their weight.

.

Galileo studied falling objects and discovered that all things fall at the same rate, despite their weight.

. Both objects fell at the same rate.

Galileo found that all objects should fall at the same rate. Air friction slows down falling objects,

Galileo found that all objects should fall at the same rate. Air friction slows down falling objects, some more than others because of their _____________

Galileo found that all objects should fall at the same rate. Air friction slows down falling objects, some more than others because of their surface area. (parachute)

Having more surface area means that there is more air pushing against the parachute, slowing it down.


He also found that objects speed up as they fall.



If air friction wasn’t a factor, all objects would accelerate toward Earth by 9.8 m/s2 (g).



If air friction wasn’t a factor, all objects would accelerate toward Earth by 9.8 m/s2 (g).

If an object falls for some time, its speed is 9.8 x time it fell.

S = g x t



Another thing he figured out was why satellites (like the moon) stay in orbit.



Another thing he figured out was why satellites (like the moon) stay in orbit. They are pulled toward the earth, but their forward motion pulls them away,

pull of gravity



Another thing he figured out was why satellites (like the moon) stay in orbit. They are pulled toward the earth, but their forward motion pulls them away, so they keep going around it.

forward motion

pull of gravity



Another thing he figured out was why satellites (like the moon) stay in orbit. They are pulled toward the earth, but their forward motion pulls them away, so they keep going around it.

forward motion

pull of gravityorbit

Using the Correct Formula:

d

s t

s

a ts = s2 – s1 s(falling) = g x t

Ex. #1: A car with a mass of 835 Kg is going 45 Km/hr along a 2500 Km road for 3 hours. How far did the car travel?


d

s t

s




d

s t

s



mass

speed

length time


d

s t

s



mass

speed

length time

What is the question asking?


d

s t

s



mass

speed

length time

What is the question asking? Distance


d

s t

s



mass

speed

length time


d = s x t


d

s t

s



mass

speed

length time


d = s x t


d

s t

s



mass

speed

length time


d = s x t = 45 x 3


d

s t

s



mass

speed

length time


d = s x t = 45 x 3 = 135 Km


d

s t

s


Ex. #2: A car with a mass of 835 Kg is going 20 m/s along a 14 foot wide road. If it slows down to 5 m/s in 3 seconds, what’s its rate of acceleration?


d

s t

s



What is the question asking?


d

s t

s



What is the question asking? acceleration


d

s t

s




a =

st


d

s t

s




a =

s s2 – s1

t t

s1

s2

time


d

s t

s




a =

s s2 – s1 5 - 20t t 3

s1

s2

time


d

s t

s




a =

s s2 – s1 5 – 20 -15 t t 3 3

s1

s2

time


d

s t

s




a =

s s2 – s1 5 – 20 -15 t t 3 3

s1

s2

time

-5 m/s2

FORCES & MOTION

FORCES & MOTIONForce – a lift, push, pull, etc. that can cause a change in an object’s motion, shape or energy level.


There are balanced forces, which are equal in strength, but


There are balanced forces, which are equal in strength, but opposite in direction.


There are balanced forces, which are equal in strength, but opposite in direction. The object does not accelerate with balanced forces.


There are balanced forces, which are equal in strength, but opposite in direction. The object does not accelerate with balanced forces.

An object can have unbalanced forces working on it, and they would make the object __________

An object can have unbalanced forces working on it, and they would make the object accelerate.


Forces are measured in Newtons.


Forces are measured in Newtons. (1 Newton is about the amount of force needed to hold up a stick of butter.)


Forces are measured in Newtons. (1 Newton is about the amount of force needed to hold up a stick of butter.)Sir Isaac Newton developed his “3 Laws of Motion” while observing the world around him.

Newton’s Laws of Motion:


First Law of Motion – “inertia”



An object at rest tends to stay at rest,



An object at rest tends to stay at rest, while an object in motion tends to stay in motion.



An object at rest tends to stay at rest, while an object in motion tends to stay in motion. Neither would change unless acted upon by an unbalanced force.




Inertia is an object’s tendency to maintain its motion.





What is the outside force that slows things down?






Friction






Friction – two surfaces rubbing together.







There may be other forces that accelerate objects also.







There may be other forces that accelerate objects also.

Seat belts are “anti-inertia” devices.

Second Law of Motion – “F = m x a”


a. An object that has more mass needs more force to accelerate it than


a. An object that has more mass needs more force to accelerate it than an object with less mass.


a. An object that has more mass needs more force to accelerate it than an object with less mass. (E.g. it takes more of a push to get a car going than a bike.)



b. If the same force is applied to 2 different objects, the one with a smaller mass will accelerate _____.



b. If the same force is applied to 2 different objects, the one with a smaller mass will accelerate more.



b. If the same force is applied to 2 different objects, the one with a smaller mass will accelerate more. (E.g. if you hit a golf ball and a bowling ball with a 5 iron, the golf ball will go faster.)




How much force is needed to accelerate a 60 Kg person on a bike by 3 m/s2?




How much force is needed to accelerate a 60 Kg person on a bike by 3 m/s2?F = m x a = 60 x 3 = 180 N

How much will a 450 Kg car accelerate if 1350 N of force are applied to it?


F = m x a


F = m x a

F

m a


F = m x a

F

m aa =

F 1350m 450 = = 3 m/s2

Third Law of Motion – “Action & Reaction”


For every action


For every action (a force exerted in some direction),


For every action (a force exerted in some direction), there is an equal and opposite reaction.



When one object exerts a force on a second object (a rocket pushing its exhaust out the back),



When one object exerts a force on a second object (a rocket pushing its exhaust out the back), the second object exerts the same force back on the first object (the exhaust pushes the rocket forward).




We often don’t see both objects move because of Newton’s 2nd Law -




We often don’t see both objects move because of Newton’s 2nd Law – the object with less mass does the most accelerating.

When you do a push-up, are you really pushing up?

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How do you know if something is in motion? Motion – changing position in space