physics :)
chapter2: force and motion
here some note for you , . this is myself , . wanna take it , just take , .
2.1 analysing linear motion
distance: total length of the path travelled (jalan panjang)
displacement: distance travelled by the obejct in specific direction (shortcut)
speed: distance travelled per unit time
= total distance travelled,d
time taken, t
velocity: rate of cange of displacement / displacement per unit time
= displacement,s
time taken
acceleration: rate of change of velocity
= change of velocity
time taken
= v-u
t
v is final velocity and u
2.3 understanding inertia
inertia: tendancy of object to remain at rest or, if moving to continue its uniform motion in straight line
positive effect of inertia:
the inertia of the tissue box make the tissue box not move when a sheet of tissue is quickly pulled from the box.
the blade of the hoe can be fitted tightly to its wooden handle
stick is use to jerk fruit from its stalk
ic skaters almost effortlessly on an icy surface
negative effect of inertia and the way to reduce it:
when the car stop immediately during an accident, the driver or passenger will throw forward and may get serous injury. = use safety belt and airbag that prevent the driver from crashing the windscreen.
aeroplane cannot stop easily. = a very long runway is required for the aeroplane to stop safely.
any log of lorry can move forward and knocking the driver compartment when the lorry stop immediately. = a steel structure is fitted in the space between the driver compartment and the load of a timber lorry
2.5 understanding the effect of force
balanced force: net force acting=zero , object at rest or moving in constant velocity
balance force ni maksudnya force yang dikenakan pada satu-satu objek tu adalah sama. Dan objek tu tiada kesan lepas force acting on it.
contoh balance force ni org tarik tali. sebelah 3 org and sebelah pun 3 org. Pastu sama berat. So tda yang menang. ni la contoh balance force. tiada kesan.
contoh balanced force:
flower pot hanging at rest(pasu digantung): the weight of the pot, w is balanced by the upward force of the tension, T of the rope. the net force acting on the flower pot is zero.
bird perching on a branch of a tree(burung bertenggek di dahan): the force of gravity , W (the bird weight) pulls it downward and the reaction of the branch, pushes the bird upward to balance the weight. the net or total force acting on the bird is zero and the bird is at rest.
golf buggy moving in a golf coarse(kereta golf berjalan di tempat golf): the engine force, which drive the buggy forward has the same magnitude but acts in the opposite direction with the air resisitance and frictional force, F. The buggy car move at constant velocity. (kereta yang bergerak dalam keadaan pecutan juga adalah balance force)
aircraft flying: aircraft flying with constant velocity. tiada pecutan.
unbalanced force: the force acting on the object do not cancel out each other . the net of unballanced force is called resultant force
unbalance force ni bermaksud force yang dikenakan adalah lebih besar atau tidak sama. contohnya, tarik tali sebelah 2org dan sebelah lagi 3org.
contoh unbalanced force:
a boy lift the objct from floor(budak mengangkat barang): a boy uses a force to lift a box from the floor. the lifting force(kuasa mengangkat) has a greater magnitude than the weight of the box. the resultant force make the box to accelerate upward.
accelerate lorry (lori memecut) : the forward upthrust engine of a lorry has a greater magnitude than the frictionel force acting on the lorry.(frictional force ialah force yang ke belakang kereta. forward upthrust engine pula force yang ke depan)
cyclist stop suddenly (penunggang basikal berhenti tiba-tiba menekan brek dan berhenti tba-tiba) : he presses the brake hard causing the magnitude of the total frictional force to be bigger than the forward force. the resultant force , F causes the bicycle to slow down or decelerate.
relationship between force , mass and acceleration
the acceleration of the object uncrease if the magnitude of the net force increased. the acceleration is directly proportional to the magnitude of the mass is constant.
the acceleration of the object decreases if the mass of the object increases when the net force remains unchanged.
the acceleration of the object is inversely proportional to the mass of the net force when the net force is constant.
newton second law: when the net external force acts on an object, the acceleration of the object is directly proportional to the net force and has a magnitude tahat is inversely proportional to its mass.
F=ma
F= force
m= mass
a= acceleration
example question: a worker pulls a block of ice on a smotth surface with a force , F. The ice has a mass of 80 kg.
if the force F = 160N, calculate the acceleration of the ice.
if the velocity of ice changes from 0 to 8m s-2in 5 s, calculate the force , F.
solution:
a. m= 80 kg ; F= 160N
using F=ma,
a=F/m
a= 160/80
a= 2 m s-2
b. kan dia bg maklumat yg velocity changes from 0 to 8 dalam masa 5 saat, so kita ble
cari dia punya acceleration.
a= v-u/t
a= (8-5)/5
a= 1.6 m s-2
F= ma
F= 80 x 1.6
F= 128 N
newton third's law: when the object exert a force on a second object, the second object exerts a force of equal magnitude but in the opposite on the first object.
contohnya, bila kwu lawan tangan ma kawan kwu, kwu akan rasa force acting on you. kwu punya kawan pun akan rasa yang sama.
contoh newton third's law:
swimmers : swimmers push the water backward with his hand and legs with force, F while the reaction force of the water, -F, pushes the swimmer forward.
example question: A car with a mass of 850 kg moving with an acceleration of 2 m s-2 . There is a frictional force of 700 N acting on the car. What is the force exerted by the engine of the car?
solution:
force exerted by the engine= (m x a) + F
= (850 x 2) + 700
= 2400 N
2.9 understanding forces in equilibrium
the forces acting on the object are in equilibrium when the resultant forces acting on the object is equal to zero. An object is at rest is in equilibrium.
resultant force: lau force yang dikenakan tu arah yang sama, so magnitude of resultant force = F1 + F2
lau resultant firce yang dikenakan dekat objek tu dari arah yang berlainan, so magnitude of resultant = F2 - F1
example 1: A trolley is been pulled by two person( boy and girl) together in the same direction. The boy pull with resultant force 2.6 N and the girl with 1.5 N.
calculate the magnitude and direction of the resultant force.
solution: oleh sebab resultant force dia dari arah yang sama, so kita guna F1 + F2
1.5 + 2.6 = 4.1 N
example 2: Farid menarik adiknya di atas troli dengan kuasa 85 N untuk bermain di luar kawasan rumah. Ayah mereka tidak membenarkan mereka untuk bermain di luar menarik troli tersebut dengan kuasa 150 N. Mereka saling menarik dari arah yang bertentangan.
calculate the magnitude oof resultant force.
solution: F1 + f2
150 - 85
=65 N
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