Preliminary Physics Module 3: Moving About Vehicles do not travel at a constant speed 1.1 Identi fy t hat a t ypic al j our ney involves speed changes: Motion can be described: as uniform motion – constant speed/velocity and as non-uniform motion – acceleration/deceleration/change in direction A typical journey involves speed changes, eg. speeding up after the engine is turned on 1.!istinguis h bet"e en i nst antaneous speed and a ver age speed of vehicles and other bodies: Instantaneous speed is the speed at a particular instant oftime A verage speed is distance travelled divided by time taen! s"d/t 1.3 !istinguish bet"een scalar and vect or #uanti ties in e#uations: A scalar #uantity speci$es si%e but not direction A vector #uantity speci$es si%e and direction &calar: mass, speed, distance, 'or, energy ( ector: force, velocity, displacement, acceleration, momentum 1.$ %ompare instantaneous speed and average speed "ith instantaneous velocity and average velocity: Instantaneous speed is speed at a particular instant in time A verage speed is total distance divided by time taen Instantaneous velocity is the velocity at a particular instant in time A verage velocity is total displacement )vector* divided by time taen 1.& !e'ne average velocity as: v av =∆ r / ∆ t: • A verage velocity is calculated using the formula v av =∆ r / ∆ t, 'here v " average velocity, ∆ r =¿ displacement )change in position* and ∆ t" time taen
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
An analysis of the e(ternal forces on vehicles helps tounderstand the e)ects of acceleration and deceleration
.1 !escribe the motion of one body relative to another:
+elative velocity is the dierence bet'een the velocity ofthe object relative to the ground and the velocity of theobserver relative to the ground
. Identify the usefulness of using vector diagrams toassist solving problems:
hange in velocity " $nal velocity – initial velocity
.3 *(plain the need for a net e(ternal force to act in orderto change the velocity of an object:
orce )* is measured in e'tons )*! it is a vector#uantity
e'ton0s $rst la' of motion: an object 'ill remain at restor move at a constant velocity unless acted upon by a net
e1ternal force )inertia is the tendency of an object toresist a change in motion*
As e'ton0s $rst la' of motion states that an object 'illremain at a constant velocity unless acted upon by a nete1ternal force, a net e1ternal force is re#uired to changethe velocity of an object
.$ !escribe the actions that must be ta+en for a vehicle tochange direction, speed up or slo" do"n:
or a vehicle to change direction, speed up or slo' do'n
there must be an unbalanced net force acting on the car
.& !escribe the typical e)ects of e(ternal forces onbodies including: friction bet"een surfaces, airresistance:
riction is a force that opposes motion and allo's tyres toget traction and allo's a car to turn
Air resistance is a type of friction that opposes car motion
.- !e'ne average acceleration as: aav=∆ v
∆t =
v−u
t :
Acceleration is a vector #uantity that measures the rateof change of velocity in ms-2
a " ∆ v /∆ t " )v-u*/t
v " u 3 at
r " ut 3 4.5at62
r " 4.5)u3v*t
v62 " u62 3 2ar
. !e'ne the terms /mass0 and /"eight0 "ith reference tothe e)ects of gravity:
Mass is the #uantity of matter that an object contains,measured in ilograms
7eight is the force applied to an object due to
gravitational attraction )gravity*, measured in e'tons
7"mg )'here g is 8.9 g" or 8.9ms-2*
. 2utline the forcing involved in causing a change in thevelocity of a vehicle "hen: coasting "ith no pressureon the accelerator, pressing on the accelerator,pressing on the bra+es, passing over an icy patch onthe road, climbing and descending hills, follo"ing acurve in the road:
oasting 'ith no pressure on the accelerator: graduallythe vehicle 'ill slo' do'n until it reaches a velocity of
magnitude of acceleration )ms-2*, v is the constant speed
)ms-* and r is the radius of the curve/circle )m*
• entripetal force )net force on an object travelling in a
circular path at a constant speed* is calculated by the
formula: F =ma=mv2
r 'here is the centripetal force )*,
m is the mass of the object )g*
. Interpret 4e"ton0s 5econd 6a" of Motion and relate it
to the e#uation: ∑ F =ma :
;he acceleration of an object is proportional to the net
force and inversely proportional to the mass
e'ton0s second la' of motion: "ma, is force inne'tons )*, m is mass in ilograms )g* and a isacceleration in meters per second )m/s62*
.17 Identify the net force in a "ide variety of situationsinvolving modes of transport and e(plain theconse#uences of the application of that net force in
terms of 4e"ton0s 5econd 6a" of Motion:
• et force is the sum of all the forces acting on a body. In
transportation the net forces is in the direction of 'here
the vehicle is travelling. ;he net force depends upon the
mass and the acceleration of the vehicle, as stated by
e'tons second la' of motion. &o if the acceleration is
ept the same for all vehicles, heavy vehicles 'ill e1ert a
greater force than lighter ones
Moving vehicles have +inetic energy and energy
transformations are an important aspect in understand
motion
3.1 Identify that a moving object possesses +inetic energy
and that "or+ done on that object can increase that
energy:
>nergy can be de$ned as the capacity to do 'or. It is ascalar #uantity
$. !e'ne impulse as the product of force and time:
Impulse is the product of force and the time interval over
'hich it acts, it is a vector #uantity and is measured in s
Impulse " t
Impulse is also change in momentum, therefore change in
momentum is e#ual to the product of force and time
$.3 *(plain "hy momentum is conserved in collisions in
terms of 4e"ton0s ;hird 6a" of Motion:
e'ton0s third la' of motion: for every action there is an
e#ual and opposite reaction
;he interaction bet'een t'o cars 'hich collide can besummarised as follo's: the total momentum of the systemof the t'o cars remains constant, the total change inmomentum is %ero, the change in momentum of the $rstcar is e#ual and opposite to the change in momentum ofthe second car, the force that the $rst car e1erts on the
second car is e#ual and opposite to the force that thesecond car e1erts on the $rst car
• Momentum is al'ays conserved.
• ;otal momentum before collision " total moment aftercollision: m u 3 m2 u2 " m v 3 m2 v2
• Momentum lost " momentum gained5afety devices are utilised to reduce the e)ects of changingmomentum
&.1 !e'ne the inertia of a vehicle as its tendency to remainin uniformmotion or at rest:
• Inertia is the tendency of an object to resist change in itsmotion. Inertia is not a force but it is a property of allobjects. ;he inertia of an object depends on the object0smass
&. !iscuss reasons "hy 4e"ton0s irst 6a" of Motion isnot apparent in many real "orld situations: