acceleration and force Physics Free Body Diagrams a
: acceleration and force Physics Free Body Diagrams a. k. a. Force Diagrams
Explanation Physics : acceleration and force Free Body Diagram • A free body diagram is a picture representation of all forces acting on an object. • We use arrows to represent the forces and indicate their direction and magnitude. • Magnitude expressed by number and arrow size.
Common Forces Physics : acceleration and force • Weight/Force of Gravity- downward force from gravity (Fg) • Applied force- Any push or pull by a person or another object (Fapp) • Normal force- force from surface object is on- always perpendicular to surface (FN) • Friction- exerted by surface- always opposite the motion (Ff ) • Air Resistance- special frictional force which acts upon objects as they travel through the air • Tension- force exerted by a rope/cable (FT) • Spring- force exerted by a spring (Fs)
Constant Velocity Physics : acceleration and force • Balanced forces. • Could be at rest or moving left, right, up or down.
Experiencing an Acceleration : acceleration and force • Unbalanced forces • Can’t tell which way it is moving, can only say which way it is experiencing an acceleration. Physics Accelerating to the right. Could be: 1. Speeding up to the right 2. Slowing down to the left Accelerating to the left. Could be: 1. Speeding up to the left 2. Slowing down to the right
Interpreting motion Physics : acceleration and force • Which of these objects could be at rest? • Which of these objects could be moving with a constant velocity? • Which of these objects could be moving right? Left? • Which of these object are accelerating?
Example Physics : acceleration and force • An apple is sitting on some books on a table. What would the FBD look like for the apple?
Example Physics : acceleration and force • A man is pulling on a box. He isn’t pulling hard enough to overcome friction and cause a net force to act on the box. What forces are acting on the box?
Example • What if the man IS pulling hard enough to cause a net force to act on the box and make it accelerate to the right? What will the diagram look like then?
Evaluation Sky Diver Physics • A skydiver jumped out of a plane 1 sec ago. Physics : acceleration and force • What would the FBD look like for his motion? Air Resistance Net force down = acceleration down Gravity
Sky Diver Physics • After some time, the skydiver has zero acceleration • What does this indicate about her speed? • Physics : acceleration and force – It is constant What is the name for this equilibrium condition of a falling object? § She has reached TERMINAL VELOCITY (air resistance =gravity) Air Resistance Net force of zero = constant velocity Gravity
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