Motion and Forces

1. Motion and Forces Test Study Guide

2. Chapter 1: Motion • Motion • 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 • 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 • 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 • (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 • 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?