Lecture 2 - Kinematics & Newton's Laws Flashcards
Define “kinematics
Study of simple description of motion only of objects (not the cause of the motion).
Kinematics is a type of mechanics. Mechanics is a branch of physics.
Define “dynamics”
Study of the causes of motion - governed by Newton’s Laws of Motion
Dynamics is a type of mechanics. Mechanics is a branch of physics.
Define “distance”
Distance is if an object travels from point S(initial) to S(final).
Distance = scalar quantity
Formula:
|dS->| = |S->(final) – S->(initial)|
Define “displacement”
Displacement is both direction and distance that the object travels.
Displacement = vector quantity with direction.
Negative (-) sign indicates that the object travelled in the opposite direction of a defined positive (+) direction.
Formula:
dS->| = |S->(final) – S->(initial)
What’s the difference between “distance” and “displacement”?
Distance calculates only distance travelled.
Distance = scalar quantity.
Displacement calculates both distance travelled AND direction of movement.
Displacement = vector quantity with direction.
i.e.
Moving object only east by 5km (+) = positive direction
Moving same object west by 7km (-) = negative direction
Total distance = 12 m
displacement = 5 – 7 = -2 m
Define “speed”
Speed is the rate of change of distance over time.
Define “velocity”
Velocity is same as speed but with a specific direction
What’s the difference between “speed” and “velocity”?
Speed is the rate of change of distance over time (no direction) = Scalar quantity
Velocity is same as speed but with a specific direction = Vector quantity
Define “acceleration”
Acceleration is the rate of change of velocity with respect to time
- Represents how much the velocity of an object **changes over time AND direction.
Acceleration due to gravity
- g = 9.81 m/s^2
- Gravity always has downward force
Average acceleration formula (we will only deal with constant acceleration)
i.e. - Acceleration is the same (no change in velocity over time) = 10m/s
Time vs Velocity
0 s | 0 m/s
1 s | 10 m/s
2 s | 20 m/s
3 s | 30 m/s
4 s | 40 m/s
5 s | 50 m/s
List the five kinematic equations, and how to use them…
- 5.
Example:
You are transporting pita bread to packaging facility on a conveyer belt. The belt is accelerating at 20m/s^2.
Starting from rest, how much time is required in order to move the bread to the packing facility located at 1000m from the starting point?
S = v0 x t + 1/2 a x t^2
Known variables:
s (distance) = 1000 m
a (acceleration) = 20m/s^2
v0 (initial velocity) - 0 m/s; starts from stationary
=Solve for T (time)
T = 10 seconds = time it will take for pita bread to move from A –> B.
Define “Force”
Force is the strength of either push or pull action.
Force = vector quantity = has direction
Define “Mass”
Mass dictates how easy or difficult it is to change an object’s velocity.
Velocity is same as speed but with a specific direction = Vector quantity
What’s the difference between “Force” and “Mass”? How are they similar?
Force is the strength of either push or pull action.
Mass dictates how easy or difficult it is to change an object’s velocity.
BOTH are considered vector quantities = have direction.
Describe Newton’s First Law of Motion
AKA “Law of Inertia” = maintaining state of motion or rest with no external force added
“in the absence of any net external force an object will keep moving at a constant speed in a straight line; or remain at rest”
Inertia = an object resisting a change in its “state of motion.”
Formula:
If (Fnet–>) = 0, then dV = 0
- i.e. state of motion will continue = throwing a ball up in the air (with NO external forces affecting the ball)
- i.e. state of rest will continue = not throwing a ball (and NO further force applied externally)
i.e. a planet’s orbit will continue if no external force is applied
Describe Newton’s Second Law of Motion
When there are external (unbalanced) forces acting on object.
“When an **external, unbalanced force **acts on an object, the object will accelerate in the same direction as the force.”
“Acceleration varies in two ways:
- directly proportional to the force * more F = more A; moving in the same direction)*
- inversely proportional to the mass (as object mass increases, the applied force is the same, but the acceleration will decrease)”
Formula:
Sum of F–> = ma–>
i.e. pen will stay on table b/c forces are balancing
gravitational force AND normal force
i.e. “–>” on up ^ and down v = “moves more –>”
i.e. If 10 N–> = 10 m/s^2, then “directly proportional”
i.e.
- if 10 N applied to a 20kg mass = 0.5 = A
vs
- if 10 N applied to a 50kg mass = 0.2 = A
Define “weight”
Weight is the gravitational force exerted on an object by the planet Earth
Formula:
W–> = m x g–>
weight equals mass x gravitational constant
Units in Newton, N
Describe Newton’s Third Law of Motion
What’s the difference between “gravitational force” and “normal force”
Gravitational = downward force
Normal force = upward force
What are the three main points of “normal force”?
- Exerted by a surface on an object (upward force)
- Acts perpendicular to, and away from, the surface at the point of contact
- Never “pulls”; always “pushes”
i.e. a mass resting on a surface
i.e. putting a heavy block on a table
i.e. surface strength will depend on the table quality/structure = normal force upwards of table holding up heavy block on table (“will the object break through the table?”)
i.e. Free-body diagram: object is on Y-axis, N is positive; W is negative
What are “Free-body diagrams?”
Free-body diagrams are used in physics theory to show the relative magnitude AND direction all forces; upon an object in a given situation.
4 Forces acting on object:
Weight (W) = downward
Normal (N) = upward
Applied (?) = rightward –>
Frictional(?) = <– leftward
i.e. Free-body diagram: object is on Y-axis, N is positive; W is negative
i.e. if (Fnet–>) = 0; means no net movement
In Free-body diagrams, what are the four forces acting on object; which direction do they go?
Forces acting on object:
Weight (W) = downward
Normal (N) = upward
Applied (?) = rightward –>
Frictional(?) = <– leftward
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