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Introduction to Forces Force is a push or pull. It is a vector quantity measured in Newtons (N) where one Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s. Thus: 1 Newton = 1 kg • m/s2 1.Type of Forces Contact Forces Action-at-a-Distance Forces Frictional Force Gravitational Force Tension Force Electrical Force Normal Force Magnetic Force Air Resistance Force Applied Force Spring Force Type of Force (and Symbol) Description of Force Applied Force An applied force is a force that is applied to an object by a person Fapp or Fa or another object. e.g. If a person is pushing a desk across the room, then there is an applied force acting upon the object. The force of gravity is the force with which the earth or other Gravity Force massively large object attracts another object towards itself. Fgrav or Fg On Earth all objects experience a downward force of gravity. The (also known as force of gravity on earth is always equal to the weight of the Weight, W) object, w: Fgrav = m * g where g = 9.8 N/kg (on Earth) and m = mass (in kg) Do not confuse weight with mass. Mass (kg) is the amount of matter that an object is made of. Weight (N) is the force of gravitational attraction. Mass is constant throughout the universe but weight changes depending on where you are. Normal Force The normal force is the support force exerted upon an object Fnorm or FN that is in contact with another stable object. e.g. If a book is sitting on a table, then the table is exerting an upward force upon the book in order to support the weight of the book. This upwards support is the normal force. On a level surface, the normal force is equal in magnitude but opposite in direction to the force of gravity. FN = - Fgrav The normal force is perpendicular to the surface. e.g. If a person leans against a wall, the wall pushes horizontally on the person. Friction Force The friction force is the force exerted by a surface as an object Ffrict or Ff moves across it (sliding friction) or makes an effort to move across it (static friction). Friction depends upon the nature of the surfaces involved and upon the degree to which they are pressed together. The maximum amount of friction force that a surface can exert upon an object can be calculated using the formula below: Ffrict = µ • Fnorm where µ = coefficient of friction (tables available) Air Resistance Air resistance is a special type of frictional force that acts upon Force objects as they travel through the air. The force of air resistance Fair or R is often opposite to the motion of an object. It is often negligible but is discussed for objects that travel at high speeds (e.g., a skydiver or a downhill skier) or for objects with large surface areas (e.g. hot air balloon). Tension Force The tension force is the force that is transmitted through a Ftens or T string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire. Spring Force Fspring or Fs The spring force is the force exerted by a compressed or stretched spring upon any object that is attached to it. adapted from physics classroom 2. Drawing Free-Body Diagrams (Draw one for EVERY force question!) 1. Represent the object as a box 2. Represent all forces as arrows The arrows are vectors so their direction is critical Start in the centre and draw outwards The size of the arrow represents the magnitude of the force 1. A textbook sits motionless on a desk. 2. A car accelerates forwards from rest. 3. A block of wood slides down an incline. Introduction to Forces Force is a ______ or ______. It is a ___________ quantity measured in Newtons (N) where one Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s. Thus: 1 Newton = 1 kg • m/s2 1.Type of Forces Contact Forces Action-at-a-Distance Forces Frictional Force Gravitational Force Tension Force Electrical Force Normal Force Magnetic Force Air Resistance Force Applied Force Spring Force Type of Force (and Symbol) Description of Force Applied Force An applied force is a force that is ___________ to an object by Fapp or Fa a person or another object. e.g. If a person is pushing a desk across the room, then there is an applied force acting upon the object. The force of gravity is the force with which the earth or other Gravity Force massively large object ___________ another object towards Fgrav or Fg itself. (also known as On Earth all objects experience a downward force of gravity. The Weight, W) force of gravity on earth is always equal to the weight of the object, w: Fgrav = m * g where g = 9.8 N/kg (on Earth) and m = mass (in kg) Do not confuse weight with mass. Mass (kg) is the ___________ _________ that an object is made of. Weight (N) is the ___________of gravitational attraction. Mass is ___________ throughout the universe but ___________ changes depending on where you are. Normal Force The normal force is the ___________ ___________exerted Fnorm or FN upon an object that is in contact with another stable object. e.g. If a book is sitting on a table, then the table is exerting an upward force upon the book in order to support the weight of the book. This upwards support is the normal force. On a level surface, the normal force is equal in magnitude but opposite in direction to the force of gravity. FN = - Fgrav The normal force is ___________ to the surface. e.g. If a person leans against a wall, the wall pushes horizontally on the person. Friction Force The friction force is the force exerted by a ___________ as an Ffrict or Ff object moves across it (___________ friction) or makes an effort to move across it (___________friction). Friction depends upon the nature of the surfaces involved and upon the degree to which they are pressed together. The maximum amount of friction force that a surface can exert upon an object can be calculated using the formula below: Ffrict = µ • Fnorm where µ = coefficient of friction (tables available) Air Resistance Air resistance is a special type of ___________ force that acts Force upon objects as they travel through the air. The force of air Fair or R resistance is often opposite to the motion of an object. It is often ___________ but is discussed for objects that travel at high speeds (e.g., a skydiver or a downhill skier) or for objects with large surface areas (e.g. hot air balloon). Tension Force The tension force is the force that is transmitted through a when Ftens or T ___________, ___________, ___________, or ___________ when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire. Spring Force Fspring or Fs The spring force is the force exerted by a compressed or stretched ___________ upon any object that is attached to it. adapted from physics classroom 2. Drawing Free-Body Diagrams (Draw one for ___________ force question!) 1. Represent the object as a box 2. Represent all forces as arrows The arrows are vectors so their direction is critical Start in the centre and draw outwards The size of the arrow represents the ___________ of the force 1. A textbook sits motionless on a desk. 2. A car accelerates forwards from rest. 3. A block of wood slides down an incline.