1. Welcome to the Physics part of Physical Science
Motion and Forces
Welcome to the Physics part of Physical Science

2. Have you ever watched a rocket launch – like the space shuttle
Have you ever watched a rocket launch – like the space shuttle? Did you ever wonder what powered the rocket or how fast it went?
Both of those questions can be related to motion, forces and mechanics.

3. Speed
The speed of an object is the distance the object travels per unit of time. Speed is a rate which tells you the amount of something that occurs or changes in one unit of time.
Speed=distance over time
Speed can be divided into two subtitles constant speed & average speed.

4. Constant & Average Speed
Constant speed is the speed that does not change.
Average speed is the total distance divided by time.
Speed is not the same as Velocity!
Speed is how fast something is going but no given or known direction – although often we can assume we know from the information given.

5. Velocity Velocity is Speed in a given direction.
If you know the velocity of an object you know its speed and its direction.
Velocity is a vector quantity. It’s also “direction-aware”. The direction of the velocity vector is simply the same as the direction which an object is moving. If going downward the velocity is downward. If going upward the velocity is upward.

6. Velocity V1 represents the initial or starting velocity
If the object starts from a rest, V1 will = 0
V2 represents the final velocity of an object
If the object ends with a stop, then V2 right at the end will be a zero, but not just a millisecond before that!
V = d / t
And this means d = vt;
and t = d / v

7. Acceleration
The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
Acceleration (a) = ΔV / Δt or-
Acceleration = force over mass

8. Let’s do an example. . .

9. Superman Leaps To the Top of a Building. . . . . . .
Let’s say the building has a height of 660 feet
His final velocity (V2) at the top is equal to 0 (cause he stopped to admire the view)
We don’t know his starting velocity (V1) or how long it took to get to the top
So – modifying the equations you are going to learn – we can get:
V2 = 2 g h where g is the acceleration due to gravity
This means V2 = 2 (32 ft/s2) (660 ft) = 205 ft/s = 140 mph!
Superman’s acceleration is definitely unearthly!

10. In addition to speed and velocity, there is a difference between Weight & Mass
Mass of an object
will not change even
Weight is a measure
Of the force of gravity
on you. Weight is a
useful measurement
of how much matter
an object has. Wt = mg
if the force of gravity
on its changes.
Mass is a
useful physical property for
describing and measuring
matter. Mass is a measurement
of inertia. The SI unit of mass is
Kilograms.

11. Mass and Weight
Your mass will remain the same – it’s how much stuff that makes you up
Weight is affected by the force of gravity – so on different planets, your mass will remain the same – but your weight will vary
(Sounds like a good diet plan for me)
Weight (Wt or W) = mass x gravity

12. Forces and Motion
Isaac Newton quantified the Laws of Motion in his 1687 work “Mathematical Principles of Natural Philosophy”
He equated motion to
forces and how they
interact on objects
He developed three
laws

13. Newton's 1st Law of Motion
An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.  
Sometimes referred to as the “Law of Inertia."
Inertia is the state of rest or resisting a force that may cause motion or a change in velocity
Galileo First theorized about this using a ball on an incline
There are two parts: one which predicts the behavior of stationary objects; and the other which predicts the behavior of moving objects . The two parts are summarized in the following diagram.

14. For example:
You and the car are traveling the same velocity – and if you brake suddenly – the car stops but you continue forward until the seatbelt stops you!

15. If there were no friction – such as air resistance, gravity, etc
If there were no friction – such as air resistance, gravity, etc. – then an object will continue in motion forever at the same velocity! This is how things move in space!

16. Example of 1st Law of Motion
Pendulum is a example for Newton's first law
This thing is often called a Newton’s Cradle
Once its in motion its always in motion.
Once its at rest its always at rest.

17. Newton's 2nd Law of Motion
The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object.
It explains the relation of force, mass & acceleration.
Force=mass x acceleration (F = ma)
The net force on an object is equal to the product of its acceleration and its mass.

18. Force Force is measured in the SI unit called a Newton (N)
1 N = 1 kg x 1 m / s2
1 N = lbs
1 lb. = N
Forces usually are in equilibrium (balanced)

19. Force
Is a push or pull
It can be divided into two subsets: unbalanced and balanced
Unbalanced force can cause an object to start or stop moving; or change its acceleration, velocity or direction
A balanced force is equal forces on an object that will not change the object’s motion

20. Forces in balance. . . The shuttle on the Fnet
launch pad is in a state of
force equilibrium – the forces
are balanced
The shuttle is in inertia or rest
with v1 = 0
Fgravity/Weight

21. When forces become unbalanced – such as when the thrust is applied. . .
Then you have
lift-off
The applied force
causes acceleration
The two SRB have a
total of 23,600,000 N of
force
(they separate at 45 km
and are recovered and
reused)

22. Acceleration
a = Δ v
Δ t
This means the acceleration rate is the change of velocity (v2 – v1) divided by the change in time (t2 – t1).
Any of these variables can be a zero
Acceleration can be either negative or positive!
Acceleration due to gravity (g) is basically the same concept, except it is up or down!

23. Acceleration Due to Gravity
agrav or just plain g, has a value of m/s2
We’ll round this off to 9.81 m/s2
Use 10 for guesstimating!
This value is for earth – your home planet may vary!
Believe it or not – agrav (g) at the equator is m/s2 and at the poles it is m/s2
Can you figure out why?

24. Free Fall Acceleration
If v1 (initial velocity is zero or the object is at rest then falls):
V2 = gt
V2 = √2gh
H = ½ gt2
H = v2 t 2

25. If v1 does not equal zero. . . V2 = v1 + g t V22 = v12 + 2 g h
H = v1t + ½ g t2
H = v2 + v1 t 2

26. Momentum (ρ) Momentum is the product of an object’s mass and velocity
It is directly proportional to mass and velocity
It’s the tendency for an object to keep in motion
p = m v
F t = m v; where F t is the impulse or change in momentum

27. Newton’s 3rd Law of Motion
A force is a push or a pull upon an object which results from its interaction with another object.
A rocket launching is a prime example of this law
Action force and
reaction force

28. Newton’s 3rd Law. . .
Basically – the law means that for every action there is an equal and opposite reaction
A rocket launch – the Fthrust downwards (action) forces the rocket upwards (reaction) against the Fgravity
Of course, there are factors such as drag (friction) which must be overcome

29. Now – it’s time for. . .
Some Rocket Science!!!!!