Principles of Projectile Motion - Teacher Notes

8/10/2019 Principles of Projectile Motion - Teacher Notes

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A) Vertical Component - gives the $rojecti"e height.

Example:f you throw a ba"" straight u$ into the air its motion is on"y vertica".

/ Horizontal Component 0 gives the $rojecti"e distance.

Example:A throw from the boundary to the wic1et 1ee$er in cric1et has a hori&onta"com$onent as we"" as a vertica" com$onent. t moves a"ong as we"" as u$.

Factors afecting trajectory:

Regard"ess of the ty$e of object that is being re"eased2 or by what means it isbeing $rojected2 they are a"" governed by 3 basic $rinci$"es)

4. Gravity2. Air resistance5. 6$eed of re"ease7. Ang"e of re"ease8. %eight of re"ease3. 6$in

Gravity

Gravity acts on a body or object to give it mass. The greater the weight of anobject2 the greater the in,uence of gravity u$on it. Gravity wi"" aect a $rojecti"eas it wi"" decrease the height the $rojecti"e can obtain. The force of gravity acts onthe object to sto$ its u$ward movement and $u"" it bac1 to earth2 "imiting thevertical com$onent of the $rojecti"e.

Air resistance



As a $rojecti"e moves through the air it is s"owed down by air resistance. Airresistance wi"" decrease the horizontal com$onent of a $rojecti"e. The eect of airresistance is very sma""2 but needs to be considered if you want to increase thehori&onta" com$onent of a $rojecti"e.

There are severa" factors that re"ate to the amount of air resistance acting on a

$rojecti"e.

a/ Surface to volume ratio. The "arger the surface to vo"ume ratio2 the moreair resistance wi"" aect the object. For e(am$"e2 a badminton shutt"e wi""have much more air resistance than a go"f ba""2 because of the ho"es in it.

b/ The surface of the object . f the surface is rough2 the air resistance wi""be greater.

c/ Speed . As s$eed increases2 so does air resistance. This is because offriction2 for e(am$"e a s$ace shutt"e.

d/ Mass. The sma""er the mass of an object2 the more air resistance wi"" aectit. For e(am$"e a feather2 com$ared to a stone.

ecause air resistance aects the hori&onta" com$onent of a $rojecti"es trajectory2the eect of it can be minimi&ed by "owering the ang"e of re"ease.

Speed of release

6$eed or ve"ocity is direct"y re"ated todistance. The greater the s$eed of re"ease2the greater the distance covered in ,ight.t is divided into two com$onents)

a) Initial Vertical Velocity ) Initial !orizontal Velocity

%aving a higher initia" vertical velocity wi""increase the height of the trajectory2resu"ting in a "onger ,ight $ath. This wou"dbe an advantage in s$orts which $rimari"yre9uire height2 such as tumb"es ingymnastics2 high jum$ and s1i jum$ing:tric1s/.

%aving a higher initia" horizontal velocity wi"" increase the "ength of the ,ight timeand therefore the distance covered. This wou"d be an advantage in s$orts which$rimari"y re9uire good distance2 such as "ong jum$2 s1i jum$ing :distance/2 andvau"ts in gymnastics.

Angle of release



The ang"e of re"ease changes the re"ationshi$ between the hori&onta" and vertica"com$onents of a $rojecti"e. The idea" ang"e of re"ease is 78 degrees2 assumingthere is no air resistance and the ta1e o and "anding $oints are the same height.

f the ang"e is greater or "ess than 78 degrees2 the distance covered in ,ight is"ess. This is because the 78 degrees is ha"f way between vertica" and hori&onta"

and wi"" ensure the greatest amount of each com$onent. f the ang"e of re"ease istoo high for a given activity2 the distance gained wi"" be $oor. f the ang"e ofre"ease is too "ow for a given activity2 the $rojecti"e wi"" be in the air for "ess time2gaining "ess distance.

n s$orting situations the ang"e of re"ease is often "ower2 around 58 degrees to 78

degrees. This is because the air resistance of the body and because the ta1eo $oint is usua""y higher than the "anding $oint2 e.g.2 "ong jum$.

Height of release

The higher the "eve" of re"ease2 the greater the distance covered in ,ight. This isbecause the higher the $rojecti"e is re"eased2 the "onger it wi"" be in the air. Thehori&onta" com$onent wi"" be acting on the $rojecti"e for "onger.

For example:A go"fer hitting a ba"" o the to$ of a hi"" wou"d hit it further than a go"fer at the

bottom of the hi"". The ba"" wi"" stay in the air "onger so wi"" have a greater chanceto gain distance. This assumes that the same go"f c"ub2 techni9ue and force isbeing used.

n jave"in2 to gain more distance2 ath"etes wi"" ho"d the jave"in u$ higher to createa greater height of re"ease.



There is a re"ationshi$ between height of re"ease and ang"e of re"ease.-As the height of re"ease increases2 the ang"e of re"ease decreases.

-As the height of re"ease increases2 the ang"e of re"ease decreases.For e(am$"e2 when shooting2 bas1etba"" $"ayers wi"" have a "ot "ower ang"e of re"ease than shorter bas1etba"" $"ayers to shoot the ba"" at the same hoo$ height.

Spin

The amount and direction of s$in acting on a $rojecti"e wi"" direct"y aect thedistance a $rojecti"e wi"" trave". The reason for this is the air $ressure acting onthe ba"".

Example:

n a tennis shot2 to$s$in gives $oorer distance com$ared to bac1s$in.Range is decreased with to$s$in.Range is increased with bac1s$in.

A to$s$in shot creates a region of high $ressure on to$ of the ba""2 and a region of "ow $ressure be"ow. Air moves from a region of high to "ow $ressure and as aconse9uence the ba"" wi"" di$ sudden"y2 decreasing the vertica" com$onent of thetrajectory and in turn2 the distance trave""ed.

n a bac1s$in shot2 a region of high $ressure is created under the ba""2 and "ow$ressure above the ba"". Air moves from high to "ow $ressure. The air $ressureacting on the ba"" wi"" cause it to stay u$ "onger2 increasing the vertica"com$onent of the trajectory2 therefore increasing the distance trave""ed.

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Principles of Projectile Motion - Teacher Notes