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TOPIC 2 : FORCE AND MOTIONFORCE AND MOTION

Linear Motion Distance Displacement Speed Velocity

Inertia Newtons first law of motion Relationship between mass and inertia

Force in equilibrium Newtons Third law of motion Resultant force

Work W=Fs

Energy Kinetic energy 2 K.E = mv Potential energy P.E = mgh Principle of conservation of energy

Momentum Acceleration P=mv Equations of motion Principle of conservation of momentum Collision and explosion

Impulse and Impulsive Force Relationship between impulsive force and impact time Negative effect reduce by Safety features in a vehicles

v u atv2 = u2 + 2 as s = ut + at2 s = (u+v) t

Power P=E/t

Force Newtons Second law of motion

Gravity Gravitational acceleration Free fall Comparison between weight and mass Factors affect elasticity Arrangement of the spring Elasticity Hookes law

Motion Graph s-t graph v-t graph

F=ma Relationship between force, mass and acceleration

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NotesPhysical Quantity Distance , d Displacement, s Speed, v Velocity, v Acceleration, a Definition Total path traveled from one location to another. SI unit metre, m Distance between two location measured along the shortest path connecting them in a specific direction. SI unit metre, m Speed, v = distance, d Time taken, t SI unit ms -1 Velocity, v = displacement, s Time taken, t SI unit ms -1 Acceleration, a = velocity, v Time taken, t SI unit ms -2

Ticker tape 1 tick = time interval between two dots Time taken to make 50 ticks = 1 s Hence 1 tick = 0.02s

- Constant velocity - zero acceleration

- increasing velocity - acceleration

- decreasing velocity - deceleration Displacement time graph

sQ R

PQ - constant velocity QR - zero velocity, object at rest RS - opposite direction with constant velocity

P

S

t vB C

Gradient = velocity

Velocity time graph AB increasing velocity, acceleration BC constant velocity, zero acceleration CD decreasing velocity, deceleration

A

D

t

Gradient = acceleration Area under graph = displacement

Inertia Newtons first law of motion Relationship between mass and inertia

tendency of the object to remain at rest or, if moving, to continue its uniform motion in a straight line Object remain at rest or in uniform motion unless its acted upon by external force The larger the mass, the larger its inertia

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Situation related to inertia

Momentum Principle of conservation of momentum Elastic collision

Momentum, p = mass, m x velocity, v

SI unit= kg m s-1

In the absence of an external force, the total momentum of a system remains unchanged.

U1

U2

V1

V2

Before collisionInelastic collisionU1 U2

After collision

V

Before collision

After collision

Explosion

Before collision

V1

V2

After collisionForce Newtons Second law of motion Relationship between a and F Relationship between a and m Impulse Impulsive force Relationship between impulsive force and impact time Situation related to impulsive force Force, F = mass, m X acceleration, a SI unit= Newton, N The rate of change of momentum is directly proportional to the applied force an acts in the direction of the force acceleration is directly proportional to force acceleration is inversely proportional to mass The change of momentum, Ft = mv mu F = mv mu , t Longer impact time impulsive force decrease Shorter impact time impulsive force increase SI unit= kg m s-1 SI unit= Newton, N

Safety features in vehicles

- Air bags - Crumple zones

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Gravitational force Free fall Weight Forces in equilibrium Newtons Third law of motion Work Kinetic energy Potential energy Principle of conservation of energy Power Hookes law

- Shatter-proof windscreen - Safety seat belt - Padded dashboard Pulled by the force of gravity tends to pull everything towards the earths centre Object is fall freely when its falling under the gravitational force only with acceleration due to gravitational force, g = 10.0 N kg-1 Gravitational force acting on the object. W=mg SI unit= Newton, N When an object is in equilibrium, the resultant force is zero. The object will either be at rest or move with constant velocity For every action there is an equal an opposite reaction Work, W = Force, F X Displacement, s SI unit= Joule, J K.E = mv 2 SI unit= Joule, J P.E = mgh SI unit= Joule, J Energy cannot be created or destroyed but can be changed from one form to another form. Power, P =

workdone timetaken

=

W t

SI unit= Watt, W

Force constant Elastic limit Graph

the extension of a spring is directly proportional to the applied force provided that the elastic limit is not exceeded F = kx, k = Force constant of the spring k = F SI unit N m-1, N cm -1 or N mm-1 x maximum force that can be applied to spring such that the spring will return to its original length when the force released F/N Elastic limit

Spring obey Hookes Law

Spring not obey Hookes Law

0Elastic potential energy Factors that effect elasticity E=kx2 =Fx -Type of material -Diameter of spring wire -Diameter of spring -Length of spring

x/cm

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Exercises1. Diagram show two watermelons fall off the table and drop on to the surface A and surface B respectively

Diagram 1 (a)

Diagram 1 (b)

a) What is mean by impulse ? . (1 mark) b) With reference to Diagram 1(a) and 1(b) i) Compare the force on the watermelons that strikes on surface A and surface B . (1 mark) ii) Compare the time of impact of the watermelons on surface A and surface B . (1 mark) iii) State the relationship between the force produced in a collision and the time of impact . (1 mark) c) Suggest a suitable material for surface B . (1 mark)

d) Explain how the driver is able to avoid serious injuries when the car stopped suddenly . . (2 mark)

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2.

a) i)

ii)

iii)

b)

When a load is attached to the spring What happen to the length of the spring ? .. (1 mark) What is the energy stored in the spring ? .. (1 mark) If the number of load is increased, what will happen to the energy in 2(a)(ii) ? .. (1 mark) The initial length of a spring is 15 cm. When a load with mass 300 g is attached to the spring, the length of the spring is 21 cm. What is the length of the spring if a load with mass 500 g is attached to the spring?

(3 mark)

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3. Diagram 3.1 and Diagram 3.2 show a student throwing a javelin using different throwing techniques. The forces used by the student are the same. The angles of projection are different.

Javelin

A Diagram 3.1

B

A Diagram 3.2(a) (i) Observe Diagram 3.1 and Diagram 3.2.

B

Compare the distance traveled by the javelin from A to B. .. (1 mark) (ii) What happens to the distance of the javelin when the angle of projection is less than the angle of projection shown in Diagram 3.2? .. (1 mark) (b) State the shape of the javelin so that it moves with minimum resistance through air .. (1 mark) (c) The force acting on the javelin is 10 N and the throwing distance 70 m. Calculate the work done by the student in Diagram 3.2.

[2 marks]

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(d) (i) State the changes of energy experienced by the javelin from A to B for techniques. .. (1 mark) (ii) State the energy produced when the javelin touches the ground. .. (1 mark)

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Answer scheme Question no. 1. a) b) (i) (ii) (iii) c) d) Suggested answer Change of momentum / product of force with time of impact Force of watermelon in diagram 1(a) is larger than force of watermelon in diagram 1 (b) Time impact on surface A is shorter than time impact on surface B The shorter the time impact, the larger the force Sponge / carpet / towel / cloth Body will be hold back by the seat belt when car stopped suddenly The seat belt will lengthen slightly, the impulsive force inflicted on the body will be less TOTAL Length increase / longer Elastic potential energy increase Extension (21-15) cm = 6 cm 300 g 6 cm 100 g 2 cm 500 g 2 x 5 = 10 cm Length of spring = 15 + 10 = 25 cm TOTAL 3 (a) (i) (ii) (b) (c) (d) (i) (ii) Further in Diagram 3.2 compare to Diagram 3.1 Decreases streamline W = 10 x 70 = 700 J Kinetic energy to potential energy to kinetic energy Sound / heat TOTAL Mark 1 1 1 1 1 1 1 7 1 1 1 1

2. a) (i) (ii) (iii) b)

1 1 6 1 1 1 1 1 1 1 7

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TOPIC 3 : FORCE AND PRESSURE

PRESSURERelationship between

Air PressurePrinciples related

Force

Area

Atmospheric Pressure

P=F ASI unit

Pascals Principleapplications

Bernoullis Principleapplications

Nm-2 / Pascal

Pressure in LiquidRelationship between

- Hydraulic Brake - Hydraulic Lift

- Bunsen Burner - Aerofoil

Archimedess Principle Buoyant Forceapplications

Depth

Density

P = gh

- Submarine - Hot Air Balloon

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NotesDefinition of Pressure Formula Pressure is force per unit area P= F A Where P = Pressure F = Force A = Area -2 Nm / Pascal (Pa) - The higher the force, th