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Forces

Forces. Change in motion?. What causes an object to start moving, stop moving, or change direction? UNBANLANCED FORCE. What is a force?. A push or pull A force is described by strength and direction The strength of a force is measured in the Newton (N) Arrows are used to represent force:.

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Forces

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  1. Forces

  2. Change in motion? • What causes an object to start moving, stop moving, or change direction? UNBANLANCED FORCE

  3. What is a force? • A push or pull • A force is described by strength and direction • The strength of a force is measured in the Newton (N) • Arrows are used to represent force:

  4. Combining forces • Most of the time, there are more than 1 force acting on an object at a time • Net force- the combination of all forces acting on an 15 N 15 N 15 N 15 N

  5. Unbalanced vs. Balanced Forces Unbalanced Forces • Result in a net force • Can cause a change in the object’s motion Balanced Forces • Equal forces acting in opposite direction • Do not cause a change in the object’s motion • They cancel each other out

  6. Draw Force Diagrams in Notebook • A book is at rest on a tabletop. Diagram the forces acting on the book • A gymnast is holding on the rings suspended from the ceiling waiting to being. • A flying squirrel is gliding (no wingflaps) from a tree to the ground at constant velocity. Consider air resistance. • A rightward force is applied to a book in order to move it across a desk at constant velocity. Consider frictional forces. Neglect air resistance

  7. Examples Continued 5. A student rests a backpack upon his shoulder. The pack is suspended motionless by one strap from one shoulder. 6. A skydiver is descending with a constant velocity. Consider air resistance 7. A force is applied to the right to drag a sled across loosely packed snow with a rightward acceleration 8. A car is coasting to the right and slowing down

  8. Formula F=m•a Force = mass x acceleration Units: Newtons (N) N=(kg)•(m/s2)

  9. Friction The force that one surface exerts on another when the two surfaces rub against each other Force that oppose motion- always in opposite direction of motion

  10. Friction… • Friction produces heat! – how have you seen this? • The amount of friction depends on: • How hard the surfaces push together (force) • Types of surfaces involved SURFACE AREA DOES NOT AFFECT THE AMOUNT OF FRICTION

  11. Static Friction • Acts on an object that are not moving • Strongest- most difficult to overcome Examples: • Desk on the floor • Parked car on the pavement

  12. Sliding Friction • Occurs when one solid surface slides over another solid surface • Not as strong as static friction Examples: • Bicycle brakes • Pushing a box along the floor

  13. Rolling Friction • Occurs when an object rolls over a surface • Not as strong as sliding friction Examples: • Shopping cart • Car traveling on the road

  14. Fluid Friction • Occurs as an object moves through a fluid • Examples: • Surf boarding in the ocean • Car as it moves through the air

  15. Gravity • Is the force that pulls objects toward each other • The law of Universal Gravitation- the force of gravity acts between all objects in the universe! • That means: any two masses exert an attractive force on each other

  16. Factors affecting gravity • Mass- a measure of the amount of matter in an object • The more mass an object has, the greater its gravitational force on other objects is • Distance • The farther apart objects are, the lesser the gravitational force between them • The sun has a gravitational force on you..why don’t you feel it? • The pencil in front of you has a gravitational force on you…why don’t you feel it?

  17. Gravitational Acceleration • The gravitational attraction of Earth causes all falling objects to have an acceleration of 9.8 m/s2 • Which direction is Earth’s gravitational force?

  18. Weight • What is it? • The gravitational force exerted on an object • W=m x g  g=a • Calculate the weight of a truck with a mass of 600 kg. G: m = 600 kg F: W=m x g g = 9.8 m/s/s Find: w = ? W.S.: w = 600kg x 9.8 m/s/s Answer: 5,880 N

  19. Mass vs. Weight • Mass is _________ • Weight is a FORCE • the more mass an object has, the stronger the gravitational force between the object and Earth. So, the more mass an object has, the more it weighs • Weight can be different if the gravitational force is different

  20. Weightlessness • When an object is influences only by the force of gravity, it is said to be in free fall.

  21. Air resistance • Air resistance acts in the opposite direct of an object’s motion • The force it opposes is GRAVITY • The amount of air resistance depends on: • Speed • Size • Shape • Terminal velocity- when the force of air resistance = weight of object no more acceleration

  22. What happens if you drop 2 objects? • What would happen if there was no air resistance? REMEMBER: • ALL OBJECTS IN FREE FALL ACCELERATE AT THE SAME RATE, REGARDLESS OF MASS!!

  23. Projectile Motion • A projectile is an object that has been projected through the air • A projectile has horizontal and vertical motion • Neglecting air resistance, all falling objects accelerate at the same rate • No matter how fast and object is moving horizontally, the force of gravity acts the same as if it was falling straight down

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