1. Motion and Forces
Test Study Guide

2. Chapter 1: Motion Motion Reference Point
Change in position, over time, relative to a reference point
Reference Point
An object to which we compare movement
Large objects (earth’s surface/the sky/trees/etc)
Can be in motion itself

3. Motion: Continued Speed Velocity
Distance an object moves in a certain amount of time
d=st d=40mph x 2hours
s=d/t s= 60yds / 30min
t=d/s t= 60m / 10m/s
Velocity
A speed in a direction
Tornado – you care what DIRECTION it’s going!
5 m/s Northeast
10 mph left
Resultant Velocity
The Overall velocity of an object
A Runner on top of a bus

4. Motion: Continued Acceleration Change in velocity (speed + direction)
Turning
A sharper turn = great acceleration
An easy turn = low acceleration
Changing speed
An increase in speed = acceleration
A decrease in speed = deceleration
Acceleration = final velocity – initial velocity
time
A=f2 – f1 t
(Practice Examples)

5. Chapter 2: Forces Force A push or a pull Net Force
Contact force – direct touching in order to cause motion
Gravity – force of attraction between 2 masses
Friction – a force that opposes motion
Net Force
The overall force acting on an object when all the forces are combined
Tug-of-war
Balanced/Unbalanced Forces
Forces balanced if net force=zero
No motion
Unbalanced forces cause motion

6. Newton’s Laws 1st Law of Motion (Law of Inertia)
An object at rest stays at rest, an object in motion stays in motion with the same velocity, until acted upon by an unbalanced force
Inertia: The resistance of an object to a change in motion (MASS)
The more mass an object has, the more force necessary to move/stop it
The less mass an object has, the less force necessary to move/stop it
SEAT BELTS in vehicles keep your inertia under control

7. Newton’s Laws: Continued
2nd Law of Motion
Acceleration depends on force and mass
F=ma
a=F/m
m=F/a
Units of Force = Newtons! (Kg x m/s2)
Imagine- Full grocery cart. If you want to accelerate it 2 m/s2 ,you could:
Push it hard (increase force) or,
Take stuff out of the cart (decrease mass)
(Practice Problems)

8. Newton’s Laws: Continued
3rd Law
Forces act in pairs
Every time one object exerts a force on another object, the second object exerts a force that is equal in size and opposite in direction back on the first object
Examples:
Swimming
Walking
ANY MOVEMENT!!!

9. Momentum A measure of Mass in Motion 2 ways to change momentum
(How much “damage” an object can do)
2 ways to change momentum
Change velocity (speed)
Change mass
Momentum = mass x velocity
P=mv
Units: kg . m/s

10. Law of Conservation of Momentum
The total momentum of a system of objects does not change, as long as no outside forces are acting on that system
Bumper cars colliding
One slows down- one speeds up
Overall momentum not changed!
Terrifying Demo
Pendulum would never stop and would hit you if there were no friction!

11. Friction Force between 2 surfaces that opposes motion Kinetic
Moving Friction
Sliding – Writing with a pencil & sledding
Rolling – Skateboarding & Driving a car
Static Friction
Non-Moving Friction
Apply a force to an object and it DOESN’T MOVE!
Walking & Pushing a wall or table

12. Friction: Continued Every object is rough (at the microscopic level)
All surfaces have a series of hills and valleys that must slide past one another
2 Factors affect the amount of friction between 2 surfaces
Roughness of surfaces
More hills and valleys means more friction
Force pushing these surfaces together
More weight = more downward force = more friction

13. Friction: Continued Harmful To Reduce Friction: Helpful
Engine parts
Scrapes
To Reduce Friction:
Lubricants
Grease
Oil
Ball Bearings
Sanding
Helpful
Walking
Brakes
Rolling/wheels
To Increase Friction
Sand on icy roads
Use rougher sandpaper
Better rubber on shoes

14. Simple Machines
Definitions
Naming Pictures (Pop Quiz)

15. Questions???
Clarifications?
Concerns?
Comments?