forces a box is being pulled across a surface by a horizontal rope. the force: applied by the rope...
TRANSCRIPT
ForcesForces
A box is being pulled across a surface A box is being pulled across a surface by a horizontal rope. The force:by a horizontal rope. The force:
applied by the rope is called _________.applied by the rope is called _________.
resisting the motion is called _________.resisting the motion is called _________.
of gravitational attraction is called of gravitational attraction is called _________._________.
applied by the surface perpendicular applied by the surface perpendicular to the object is called _________.to the object is called _________.
ForcesForces
A box is being pulled across a surface A box is being pulled across a surface by a horizontal rope. The force:by a horizontal rope. The force:
applied by the rope is called applied by the rope is called tensiontension..
resisting the motion is called resisting the motion is called frictionfriction..
of gravitational attraction is called of gravitational attraction is called weightweight..
applied by the surface perpendicular to applied by the surface perpendicular to the object is called the object is called the normal forcethe normal force..
An Introduction to Forces: An Introduction to Forces: Student Learning GoalStudent Learning Goal
The student will use free-body The student will use free-body diagrams to determine the net force diagrams to determine the net force on an object and be able to apply on an object and be able to apply Newton’s 1Newton’s 1stst Law to explain the Law to explain the effect of forces acting on objects. effect of forces acting on objects. (C2.2 and C3.3)(C2.2 and C3.3)
FBDs and FBDs and Newton’s 1Newton’s 1stst Law Law
SPH3USPH3U
Free-Body DiagramsFree-Body Diagrams
Usually an object will have more than Usually an object will have more than one force acting upon it.one force acting upon it.
Free-Body DiagramsFree-Body Diagrams
Usually an object will have more than Usually an object will have more than one force acting upon it. A one force acting upon it. A free-free-body diagrambody diagram (FBD) shows all the (FBD) shows all the forces acting on an objectforces acting on an object
Free-Body DiagramsFree-Body Diagrams
Usually an object will have more than Usually an object will have more than one force acting upon it. A one force acting upon it. A free-free-body diagrambody diagram (FBD) shows all the (FBD) shows all the forces acting on an object – and forces acting on an object – and onlyonly the forces acting on the object.the forces acting on the object.
Free-Body DiagramsFree-Body Diagrams
Usually an object will have more than Usually an object will have more than one force acting upon it. A one force acting upon it. A free-free-body diagrambody diagram (FBD) shows all the (FBD) shows all the forces acting on an object – and forces acting on an object – and onlyonly the forces acting on the object.the forces acting on the object.
A representation of the object is A representation of the object is drawn in the centre of the diagramdrawn in the centre of the diagram
Free-Body DiagramsFree-Body Diagrams
Usually an object will have more than Usually an object will have more than one force acting upon it. A one force acting upon it. A free-free-body diagrambody diagram (FBD) shows all the (FBD) shows all the forces acting on an object – and forces acting on an object – and onlyonly the forces acting on the object.the forces acting on the object.
A representation of the object is A representation of the object is drawn in the centre of the diagram drawn in the centre of the diagram and the forces acting on it are drawn and the forces acting on it are drawn as arrows pointing outwards.as arrows pointing outwards.
Free-Body DiagramsFree-Body Diagrams
Usually an object will have more than one Usually an object will have more than one force acting upon it. A force acting upon it. A free-body free-body diagramdiagram (FBD) shows all the forces (FBD) shows all the forces acting on an object – and acting on an object – and onlyonly the forces the forces acting on the object.acting on the object.
A representation of the object is drawn in A representation of the object is drawn in the centre of the diagram and the forces the centre of the diagram and the forces acting on it are drawn as arrows acting on it are drawn as arrows pointing outwards. The arrows must be pointing outwards. The arrows must be labelled!labelled!
FBD: Example 1FBD: Example 1
A ball is falling downward through the A ball is falling downward through the air. Draw a FBD for the ball.air. Draw a FBD for the ball.
FBD: Example 1FBD: Example 1
A ball is falling downward through the A ball is falling downward through the air. Draw a FBD for the ball.air. Draw a FBD for the ball.
FBD: Example 1FBD: Example 1
A ball is falling downward through the A ball is falling downward through the air. Draw a FBD for the ball.air. Draw a FBD for the ball.
Fg
FBD: Example 1FBD: Example 1
A ball is falling downward through the A ball is falling downward through the air. Draw a FBD for the ball.air. Draw a FBD for the ball.
Fg
Fair
FBD: Example 2FBD: Example 2
A book is being pushed rightward A book is being pushed rightward across a table. Draw a FBD for the across a table. Draw a FBD for the book.book.
FBD: Example 2FBD: Example 2
A book is being pushed rightward A book is being pushed rightward across a table. Draw a FBD for the across a table. Draw a FBD for the book.book.
FBD: Example 2FBD: Example 2
A book is being pushed rightward A book is being pushed rightward across a table. Draw a FBD for the across a table. Draw a FBD for the book.book.
FA
FBD: Example 2FBD: Example 2
A book is being pushed rightward A book is being pushed rightward across a table. Draw a FBD for the across a table. Draw a FBD for the book.book.
FAFf
FBD: Example 2FBD: Example 2
A book is being pushed rightward A book is being pushed rightward across a table. Draw a FBD for the across a table. Draw a FBD for the book.book.
Fg
FAFf
FBD: Example 2FBD: Example 2
A book is being pushed rightward A book is being pushed rightward across a table. Draw a FBD for the across a table. Draw a FBD for the book.book.
Fg
FN
FAFf
Net ForceNet Force
FBDs are drawn to help determine the FBDs are drawn to help determine the net force net force (the sum of all forces) (the sum of all forces) acting on an object.acting on an object.
Resolve all vertical and horizontal Resolve all vertical and horizontal vectors and determine the resultant.vectors and determine the resultant.
FBD: Example 2 with FBD: Example 2 with NumbersNumbers
A book is being pushed across a table with a A book is being pushed across a table with a force of 5 N [right]. The force of friction force of 5 N [right]. The force of friction is 2 N [left], the gravitational force is 10 is 2 N [left], the gravitational force is 10 N [down], and the normal force is 10 N N [down], and the normal force is 10 N [up]. Find the net force on the book.[up]. Find the net force on the book.
FBD: Example 2 with FBD: Example 2 with NumbersNumbers
A book is being pushed across a table with a A book is being pushed across a table with a force of 5 N [right]. The force of friction force of 5 N [right]. The force of friction is 2 N [left], the gravitational force is 10 is 2 N [left], the gravitational force is 10 N [down], and the normal force is 10 N N [down], and the normal force is 10 N [up]. Find the net force on the book.[up]. Find the net force on the book.
Fg = 10 N
FA = 5 NFf = 2 N
FN = 10 N
FBD: Example 2 with FBD: Example 2 with NumbersNumbers
A book is being pushed across a table with a A book is being pushed across a table with a force of 5 N [right]. The force of friction is 2 force of 5 N [right]. The force of friction is 2 N [left], the gravitational force is 10 N [down], N [left], the gravitational force is 10 N [down], and the normal force is 10 N [up]. Find the and the normal force is 10 N [up]. Find the net force on the book.net force on the book.
Horizontal forces: FHorizontal forces: FAA + F + Fff = 5 N + (- 2 N) = 3 N = 5 N + (- 2 N) = 3 N
Vertical forces: FVertical forces: Fgg + F + FNN = (- 10 N) + (10 N) = 0 = (- 10 N) + (10 N) = 0
The net force FThe net force Fnetnet = 3 N [right] = 3 N [right]
Zero Net Force: ExampleZero Net Force: Example
A weightlifter holds a weight above A weightlifter holds a weight above his head by exerting a force of 1.6 his head by exerting a force of 1.6 kN [up]. The force of gravity acting kN [up]. The force of gravity acting on the weight is 1.6 kN [down]. on the weight is 1.6 kN [down]. Draw a FBD of the weight. What is Draw a FBD of the weight. What is the net force on the weight?the net force on the weight?
Zero Net Force: ExampleZero Net Force: Example
FA=1.6 kN
Fg=1.6 kN
Zero Net Force: ExampleZero Net Force: Example
The net force is zero.The net force is zero.
FA=1.6 kN
Fg=1.6 kN
Newton’s First Law of Newton’s First Law of MotionMotion
If there is no If there is no netnet force acting on an force acting on an object, the object will remain at restobject, the object will remain at rest
Newton’s First Law of Newton’s First Law of MotionMotion
If there is no If there is no netnet force acting on an force acting on an object, the object will remain at restobject, the object will remain at rest
Newton’s First Law of Newton’s First Law of MotionMotion
If there is no If there is no netnet force acting on an force acting on an object, the object will remain at rest object, the object will remain at rest or will keep moving at the same or will keep moving at the same constant velocity.constant velocity.
Newton’s First Law of Newton’s First Law of MotionMotion
If there is no If there is no netnet force acting on an force acting on an object, the object will remain at rest object, the object will remain at rest or will keep moving at the same or will keep moving at the same constant velocity.constant velocity.
(Conversely, if an object is at rest or is (Conversely, if an object is at rest or is moving at constant velocity, there is moving at constant velocity, there is no net force acting upon it.)no net force acting upon it.)
InertiaInertia
This is the principle of This is the principle of inertiainertia, first , first articulated by Galileo:articulated by Galileo:
Newton’s First Law of Newton’s First Law of MotionMotion
QuestionQuestion: An object is pushed along at : An object is pushed along at constant velocity by a force of 5 N constant velocity by a force of 5 N [left]. What is the force of friction [left]. What is the force of friction acting on the object?acting on the object?
Newton’s First Law of Newton’s First Law of MotionMotion
QuestionQuestion: An object is pushed along at : An object is pushed along at constant velocity by a force of 5 N constant velocity by a force of 5 N [left]. What is the force of friction [left]. What is the force of friction acting on the object?acting on the object?
If the velocity is constant, there is no If the velocity is constant, there is no net force, so the force of friction must net force, so the force of friction must be equal in magnitude and opposite in be equal in magnitude and opposite in direction to the applied force:direction to the applied force:
Newton’s First Law of Newton’s First Law of MotionMotion
Question: An object is pushed along at : An object is pushed along at constant velocity by a force of 5 N [left]. constant velocity by a force of 5 N [left]. What is the force of friction acting on the What is the force of friction acting on the object?object?
If the velocity is constant, there is no net If the velocity is constant, there is no net force, so the force of friction must be force, so the force of friction must be equal in magnitude and opposite in equal in magnitude and opposite in direction to the applied force:direction to the applied force:
FFff = 5 N [right] = 5 N [right]
More PracticeMore Practice
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LawLaw