projectile motion a projectile is an object on which the only force acting is ______ and the...

Projectile MotionProjectile Motion

A projectile is an object on which the A projectile is an object on which the only force acting is ______ and the only force acting is ______ and the direction of this force is always direction of this force is always _____._____.

(In real life, a projectile will also have (In real life, a projectile will also have ______ or ___________ acting on it and ______ or ___________ acting on it and the direction of this force is always the direction of this force is always _____________________.)_____________________.)

Projectile MotionProjectile Motion

A projectile is an object on which the A projectile is an object on which the only force acting is only force acting is gravitygravity and the and the direction of this force is always direction of this force is always downdown..

(In real life, a projectile will also have (In real life, a projectile will also have frictionfriction or or air resistanceair resistance acting on it acting on it and the direction of this force is always and the direction of this force is always opposite the direction of motionopposite the direction of motion.).)

An Introduction to Forces: An Introduction to Forces: Student Learning GoalStudent Learning Goal

The student will The student will analyse, in analyse, in quantitative terms, the forces acting quantitative terms, the forces acting on an object, and use free-body on an object, and use free-body diagrams to determine net force on diagrams to determine net force on the object in one dimensionthe object in one dimension. (B2.9). (B2.9)

An Introduction An Introduction to Forcesto Forces

SPH4CSPH4C

A DefinitionA Definition

A A forceforce is a push or a pull. is a push or a pull.



It is a vector quantity and is symbolized It is a vector quantity and is symbolized by:by:



It is a vector quantity and is symbolized It is a vector quantity and is symbolized by:by:

F



It is a vector quantity and is symbolized by:It is a vector quantity and is symbolized by:

In the SI system, force is measured in In the SI system, force is measured in Newtons (N).Newtons (N).

1 N = 1 kg m/s1 N = 1 kg m/s22

F

Applied ForceApplied Force

Applied ForceApplied Force is a is a general term for any general term for any contact force, e.g.contact force, e.g.

F A



TensionTension

F or TT

F A



TensionTension

FrictionFriction

F or TT

F A

F or Ff fr



TensionTension

FrictionFriction

Normal ForceNormal Force

F or TT

FN

F A

F or Ff fr

TensionTension

Tension is the force Tension is the force exerted by strings, exerted by strings, ropes, cables, etc. ropes, cables, etc. attached to an object.attached to an object.

TensionTension

Tension is the force Tension is the force exerted by strings, exerted by strings, ropes, cables, etc. ropes, cables, etc. attached to an object.attached to an object.

The tension along the The tension along the string is constant.string is constant.

FrictionFriction

Friction acts to oppose any Friction acts to oppose any (attempted) motion.(attempted) motion.

FrictionFriction


Static friction: the force that Static friction: the force that prevents a stationary object from prevents a stationary object from starting to movestarting to move

Fs

FrictionFriction



Kinetic friction: the force that acts Kinetic friction: the force that acts against an object’s motionagainst an object’s motion

FsFk

FrictionFriction




Air resistance (drag): friction on an Air resistance (drag): friction on an object moving through airobject moving through air

FsFk

Fa ir

FrictionFriction

Friction acts to oppose any (attempted) Friction acts to oppose any (attempted) motion.motion.

Static friction: the force that prevents a Static friction: the force that prevents a stationary object from starting to movestationary object from starting to move


Air resistance (drag): friction on an Air resistance (drag): friction on an object moving through air (many physics object moving through air (many physics problems with neglect this)problems with neglect this)

FsFk

Fa ir


The normal force acts to keep objects The normal force acts to keep objects apart.apart.


The normal force acts to keep objects The normal force acts to keep objects apart.apart.

i.e. if you push on a wall, the wall will i.e. if you push on a wall, the wall will exert a normal force on your hand exert a normal force on your hand that prevents your hand from that prevents your hand from pushing through the wall.pushing through the wall.

Action-at-a-Distance Action-at-a-Distance ForcesForces

There exist forces for which There exist forces for which contact between objects is contact between objects is not necessary. These forces not necessary. These forces are called are called action-at-a-action-at-a-distance forcesdistance forces..


There exist forces for which There exist forces for which contact between objects is contact between objects is not necessary. These forces not necessary. These forces are called are called action-at-a-action-at-a-distance forcesdistance forces. .

One example is gravitational One example is gravitational force, the force of attraction force, the force of attraction between between allall objects with objects with mass.mass.

Fg


There exist forces for which There exist forces for which contact between objects is not contact between objects is not necessary. These forces are necessary. These forces are called called action-at-a-distance action-at-a-distance forcesforces. .

One example is gravitational force, One example is gravitational force, the force of attraction between the force of attraction between allall objects with mass. objects with mass.

(The gravitational force the Earth (The gravitational force the Earth exerts on an object is called its exerts on an object is called its weightweight.).)

Fg

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.


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


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



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.


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.



Fg



Fg

Fair


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



FAFf



Fg

FAFf



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.


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


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]

More PracticeMore Practice

Estimating and Measuring ForcesEstimating and Measuring Forces

projectile motion a projectile is an object on which the only force acting is ______ and the...

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