 # Forces and Free Body Diagrams

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Forces and Free Body Diagrams

Force and Free Body Diagram
Free-body diagrams (F.B.D.): Diagrams that show the relative magnitude and direction of all forces acting upon an object in a given situation.

Contact and Action at a Distance Forces
Contact forces - forces that result when two interacting objects are physically contacting each other. Action-at-a-distance forces - forces that result even when the two objects are not in physical contact with each other.

Types of Forces Name of Force Symbol Description of the force.
Force of Gravity Fgrav The force with which the earth or other massively large object attracts another object towards itself. Is always directed downwards Applied Force Fapp A force which is applied to an object by a person or another object.

Types of Forces Name of Force Symbol Description of the force.
Normal Force FNorm The support force exerted upon an object which is in contact with a surface of a stable object. Friction Force Ffric The force exerted by a surface as an object moves across it or makes an effort to move across it. Directed opposite of motion.

Types of Forces Name of Force Symbol Description of the force.
Air Resistance Force Fair A frictional force which acts upon objects as they travel through the air. Directed opposite of motion. Tension Force Ften The force which is transmitted through a string, rope, cable, or wire when it is pulled.

Types of Forces Name of Force Symbol Description of the force.
Spring Force Fspring The force exerted by a compressed or stretched spring.

Contact Forces Applied Force Surface Force Friction Force Air Resistance Force Tension Force Spring Force Action-at-a-Distance Forces Force of Gravity Electrical Force Magnetic Force

Free Body Diagrams The direction of the arrow shows the direction that the force is acting. The size of the arrow in a free-body diagram reflects the magnitude of the force. Each force is labeled to indicate the exact type of force. Represent the object by a box (or drawing) and draw the force arrow from the center of the box outward in the direction that the force is acting.

Free Body Diagrams

Free Body Diagram Homework Examples

Gravity and Surface Force
Gravity and Tension Gravity 1. A lamp is at rest on a table top. 2. A disco ball is suspended motionless from the ceiling by a cable. 3. An egg is free-falling from a nest in a tree. Neglect air resistance.

4. An egg is falling from a nest but still accelerating
4. An egg is falling from a nest but still accelerating. Include air resistance. 5. A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant velocity. Consider air resistance. 6. A leftward force is applied to a book in order to move it across a desk at constant velocity. Consider frictional forces. Neglect air resistance. Gravity and air resistance Gravity, applied, surface and friction

8. A soft ball as it is being hit by a bat.
7. A college student rests a backpack upon her shoulders. The pack is suspended motionless by two straps from her shoulders. 8. A soft ball as it is being hit by a bat. 7. Gravity and tension 8. Gravity and Applied

9. A softball is moving directly upwards after having been batted
9. A softball is moving directly upwards after having been batted. Diagram the forces acting upon the softball as it rises upward towards its peak and as it starts to fall back down from it peak (two different free body diagrams). Include air resistance. 10. A car is coasting to the right and slowing down. 9. Gravity and air resistance Gravity, surface and friction