unit 5: motion, forces & simple machines. section 1: what is motion? objectives: define motion ...
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Unit 5:Motion, Forces & Simple Machines
Section 1: What is Motion? Objectives:
Define motionCalculate speed, velocity, and acceleration
Assessment Anchor:S8.C.3.1
What is motion?
Motion – occurs when the distance between two objects changes
Ex: Driving down the road
Running around the field
Jumping up and down
Distance
The space between two objects Units: miles, meters, blocks, feet, yard
Distance
Speed
How much the distance changes in a certain amount of time
Units: mph, m/s, blocks/min
ds
t
Velocity:
Speed in a given direction
Ex: 60 mph = speed
60 mph north = velocity
Acceleration
Change in speed over timeUnits: mph/s, m/s2
change in speeda=
t
Momentum
An object’s momentum is equal to its mass times its velocity
p = mvmomentum
Conservation of Momentum
In a collision, the total momentum of all objects is conserved
Sample Problem #1
It takes you 2 hours to travel 120 miles on the Interstate. What is your speed?
Sample Problem # 2
If you’re driving down the road at 35 mph for 3 hours, how much distance will you cover?
Sample Problem #3
You need to speed up from 10 mph to 50 mph in 5 seconds. What acceleration is necessary to accomplish this?
Sample Problem #4
If an object has a mass of 10 kg and a velocity of 5 m/s North, what is the momentum of that object?
Section 2: Motion Graphs Objectives:
Use a displacement vs. time graphUse a velocity vs. time graph
Assessment Anchor:S8.C.3.1
Moving on to Graphs…
Why do we use graphs? To represent information more easily than writing it
all out
Parts of a graph
Two types of graphs
Distance vs. time Velocity vs. time
d (m)
t (s) t (s)
v (m/s)
Interpreting a Distance vs. Time Graph
d(m)
t(s)
Interpreting a Velocity vs. Time Graph
v(m/s)
t(s)
Section 3: Forces and Newton’s Laws Objectives:
Identify the types of forcesApply Newton’s Laws of Motion
Assessment Anchor:S8.C.3.1
Definition of force
Force – any push or pull on an object
Units:
2
m1 kg = 1 N
s
Newton
Examples of Forces
Some forces…
Two types of forces
BalancedWon’t cause an object to move
UnbalancedCan cause an object to move
Free Body Diagrams
Balanced Forces
Free Body Diagrams
Unbalanced Forces
Newton’s 1st Law of Motion
An object in motion will stay in motion and an object at rest will stay at rest; unless acted on by an unbalanced force
Explanation: To change the motion of an object, you need to apply an unbalanced force.
Newton’s 2nd Law of Motion
The force on an object is equal to the object’s mass times its acceleration
Explanation: F = ma
Newton’s 3rd Law of Motion
For every action force, there is an equal and opposite reaction force.
Explanation: If I push on an object, that object pushes back on me with the same amount of force.
Section 4: Work Objectives:
Define workCalculate the work done by an object
Assessment Anchor:S8.C.3.1
The “Scientific” Definition…
Work – when a force is exerted on an object that moves the object some distance Units: Newton – meter (Nm)
In other words…
To do “work”, you need to:Apply a force ANDMove the object some distance ANDSome of the force needs to be in the direction
of the motion
In equation form…
W=Fd
Sample Problem #1
If it takes 3 N to move an object a distance of 4 m, how much work is done?
Sample Problem #2
You apply a force of 20 N to an object, but it does not move. How much work is done on the object?
Section 5: Simple Machines Objectives:
Identify simple machinesExplain the mechanical advantage of simple
machines
Assessment Anchor:S8.C.3.1
Why do we use machines?
1. Change amount of force necessary
2. Change distance you apply force
3. Change direction you apply force
Input vs. Output Force
Input Force – the force you exert on a machine
Output Force – the force exerted by the machine
Mechanical Advantage
Mechanical Advantage tells us how much the machine helps.
output forceMA =
input force
More on Mechanical Advantage
If: MA > 1…force is multiplied
MA = 1…different direction
MA < 1…distance is multiplied
Sample Problem
Find the mechanical advantage of a machine that delivers an output force of 12 N when an input force of 3 N is applied.
Inclined Plane
Flat slanted surface
Requires less effort over a longer distance
Ideal Mechanical Advantage for Inclined Plane
IMA = length of incline height of incline
8 m
2 m
Wedge
Device that is thick at one end and tapers to a thin edge at other end
Screw
An inclined plane wrapped around a cylinder
Lever
A rigid bar that is free to pivot or rotate about a fixed point
Ideal Mechanical Advantage for Lever
IMA = distance from fulcrum to input force distance from fulcrum to output force
inputoutput
4 m 2 m
fulcrum
Wheel and Axle
Two circular or cylindrical objects, fixed together that rotate about a common axis
Pulley
A grooved wheel with a rope wrapped around it
Ideal Mechanical Advantage for Pulley
IMA = number of sections of rope that support object