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