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Forces

Forces. What is a FORCE????. A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects .

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Forces

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  1. Forces

  2. What is a FORCE???? • A force is a push or pull upon an object resulting from the object's interaction with another object. • Whenever there is an interaction between two objects, there is a force upon each of the objects. • For simplicity sake, all forces (interactions) between objects can be placed into two broad categories: • contact forces, and • forces resulting from action-at-a-distance

  3. Forces • Contact forces are those types of forces that result when the two interacting objects are perceived to be physically contacting each other. • Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces. • Action-at-a-distance forces are those types of forces that result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation. • Examples of action-at-a-distance forces include gravitational forces. For example, the sun and planets exert a gravitational pull on each other despite their large spatial separation.

  4. Force Force is a quantity that is measured using the standard metric unit known as the Newton. A Newton is abbreviated by an "N." To say "10.0 N" means 10.0 Newton of force. One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s.

  5. Force • Force – the acceleration of an object with a certain mass. • F = ma • where F (measured in N for Newtons) is the Force, • m=mass (in kg) and • a = acceleration (in m/s2 or m/s/s) • 1N = 1 kg*m/s2

  6. Forces What is the difference between force from gravity and acceleration due to gravity? Acceleration due to gravity is the rate at which an object is “pulled” towards the Earth…..9.8m/s2 Force from gravity is the attraction between the Earth and an object. F = mg Where g=gravity= 9.8 m/s2

  7. Mass vs weight • What is the difference between mass and weight? • Mass=how much matter makes up an object • Measured in kg • Weight=the effect gravity has on an object’s mass • Measured in N

  8. Types of Forces

  9. Types of Forces Drag force: force exerted on an object through a fluid Air Resistance: a specific type of drag force exerted on an object by the air Friction Force: the resistance of a surface to motion Tension Force: the force on a rope or cord Spring force: the force exerted by a compressed or stretched spring upon any object that is attached to it. Applied Force: a direct push or pull on an object

  10. Types of Forces • Normal Force: the support force exerted upon an object that is in contact with another stable object. • For example, if a book is resting upon a surface, then the surface is exerting an upward force upon the book in order to support the weight of the book. • On occasions, a normal force is exerted horizontally between two objects that are in contact with each other. • For instance, if a person leans against a wall, the wall pushes horizontally on the person. • The normal force is exerted perpendicular to the surface

  11. When in doubt….draw it out! • Pictures/diagrams are your BEST FRIEND in physics • Diagrams can help us visualize all the different forces acting on an object at any given time • Forces in opposite directions will have opposite signs • The direction of motion is considered to be the positive direction

  12. Drawing forces • Draw the following scenarios and label any and all forces you think are acting on the object • A person sitting in a chair • A ball being thrown vertically in the air • A person swimming • A car being driven down the road • A child ice skating • A child sitting on a swing • A person skating down a hill

  13. Free Body Diagrams Drawing the whole picture can get a little complicated….so we use what are called free body diagrams Free-body diagrams are diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation. The size of the arrow in a free-body diagram reflects the magnitude of the force. The direction of the arrow shows the direction that the force is acting.

  14. Free Body Diagrams It is generally customary in a free-body diagram to represent the object by a box and to draw the force arrow from the center of the box outward in the direction that the force is acting.

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