Unit 5: Motion, Forces & Simple Machines

Section 1: What is Motion? Objectives:  Define motion  Calculate 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

Velocity: Speed in a given direction Ex: 60 mph = speed 60 mph north = velocity

Acceleration Change in speed over time  Units: mph/s, m/s 2

Momentum An object’s momentum is equal to its mass times its velocity p = mv momentum

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 graph  Use 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) 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 forces  Apply Newton’s Laws of Motion Assessment Anchor:  S8.C.3.1

Definition of force Force – any push or pull on an object Units: Newton

Examples of Forces

Some forces…

Two types of forces Balanced  Won’t cause an object to move Unbalanced  Can cause an object to move

Free Body Diagrams Balanced Forces

Free Body Diagrams Unbalanced Forces

Newton’s 1 st 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 2 nd Law of Motion The force on an object is equal to the object’s mass times its acceleration Explanation: F = ma

Newton’s 3 rd 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 work  Calculate 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 AND  Move the object some distanceAND  Some of the force needs to be in the direction of the motion

In equation form…

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 machines  Explain 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.

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 input output 4 m2 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