Download Motion - RowesPhysicalScience

How Do Things Move?
1. What is motion? Position, reference point, distance, time, distance time graphs.
Motion is an object’s change in position relative to a reference point.
The object that appear to stay in place is a reference point.
Speed is the distance traveled by an object divided by the time taken to travel.
SI unit for speed: Meter per second (m/s)
Average Speed = total distance
total time
2. How is motion measured? Speed, introduce mathematical equation, compute slope of
distance/time graph to find speed, discuss significance of slope (just by eyeballing),
discuss average speed.
**Practice Problem: What is your average speed if you take 0.5 h to walk 4,000 m?
(4,000)
(.5)
= 8,000 m/h
3. How is velocity different from speed? Vector, velocity time graph analysis
Velocity is the speed of an object in a particular direction.
– Ex: Plane’s velocity is 400 km/h south.
Vector – Numerical value & Direction
4. How is changing velocity measured? Acceleration, introduce mathematical equation,
use velocity time graph to find slope to determine acceleration, discuss significance of
slope (just by eyeballing)
An object’s velocity changes if either its speed or direction changes.
Avg. Acceleration =
final velocity – starting velocity
time it takes to change velocity
**Practice Problem: What is the average acceleration of a subway train that speeds up
from 9.6 m/s to 12 m/s in 0.8 s on a straight-line section of track?
12 m/s - 9.6 m/s
0.8 s
= 3 m/s2
Change of Velocity
Delta V = gravity(g) x time(t); where Acceleration of gravity = 9.8 m/s2 and time it takes to fall.
5. What is a force? Push, pull, gravity, friction, balanced and unbalanced forces, net force,
vector
You can change an objects motion by pushing it, pulling it, nudging it, or by any
number of other things; all of which are referred to as air forces.
Friction is a force that opposes motion between two surfaces that are in contact.
Static Friction – A force is applied to an object but does not move.
Kinetic Friction – Moving surfaces. Ex: Anything with wheels
Gravity is a force of attraction between objects that is due to their masses. Gravity –
The Earth’s pull on a object.
Gravitational force increases as mass increases.
Gravitational forces decreases as distance increases.
Scientist express forces using a unit called newton (N)
The net force is the combination of all the forces acting on an object.
The same balanced force = no motion or no force at all
Unbalanced force = motion
6. What governs the movement of a single object’s motion (balanced forces)? Newton’s
First Law, inertia, relationship of inertia to mass
Newton’s Law of Motion
1st Part = Objects tend to remain at rest unless a force acts on them
2nd Part = Objects in motion tend to stay in motion until a force acts on them.
Inertia – An object’s tendency to keep on doing what it’s doing
*It’s hard to change the motion of an object with lots of inertia (a bowling ball or an
elephant)
7. What happens to the movement of an object acted upon by an unbalanced forces?
Newton’s second law, relates force, mass, and acceleration, F = ma, experimentally
determine, graph, find acceleration by graphing force versus mass
F = ma (force is equal to mass times acceleration)
Small Force = Small Acceleration
Large Force = Large Acceleration
Same Force applied to small mass = large acceleration (Beach Ball)
Same Force applied to large mass = small acceleration (Bowling Ball)
8. What happens when two objects in motion interact? Newton’s Third Law, momentum,
mathematically compute momentum, p = mv, action/reaction, law of conservation of
momentum
Newton’s Third Law of Motion: For every action (force) there is an equal but opposite reaction.
Momentum: "mass in motion”
Equation: p = m * v
Unit: kg*m/s
**Practice Problem: Determine the momentum of a ...
a.) 60 kg halfback moving eastward at 9 m/s.
p = 540 kg*m/s, east