(i)

Surface tension

(ii)

Substances to reduce surface tension

1. Kerosene
2. Oil
3. Soap/detergent
4. Diesel
5. Petrol

i)

A force is that which changes a body's state of rest or uniform motion in a straight line

OR

A force is a pull or a push on an object.

ii)

Effects of forces on the body

1. It changes direction of a moving body
2. It increases speed of a body or causes a body to accelerate
3. It decreases the speed of a body or causes a body to decelerate
4. It causes a stationary body to move
5. It causes a moving body to stop
6. It causes deformation/changes the shape of a body

(i)

Pressure is defined as force per unit area applied in a direction perpendicular/normal to the surface of the object.

OR

Pressure = $\frac{\mathrm{Force\; (F)}}{\mathrm{Area\; (A)}}$

(ii)

Why it is important to sharpen a knife before use

When a knife is sharpened, the cutting edge becomes smaller so that with a little force applied, a larger pressure is exerted for cutting to be easier.

(i)

Friction is the force that opposes the relative (sliding) motion between two surfaces in contact with one another.

(ii)

Bad effects/Disadvantages of friction

1. It causes wear and tear
2. It generates heat in machine parts
3. Opposes motion

(iii)

Advantages of friction

1. Prevents slipping when walking
2. Enables holding of materials
3. Vehicle brake system
4. Helps ignition of matches
5. Helps to grind substances to powder
6. Helps nails to stick into wood/wall
7. Helps to sharpen tools

(i)

Pressure is the force acting perpendicularly/normally over certain surface

OR

Pressure is the force acting perpendicularly/normally per unit area

Pressure (P) = $\frac{\mathrm{Force\; (F)}}{\mathrm{Area\; (A)}}$

(ii)

Applications of pressure in everyday life

1. Opening a tin of milk with a nail
2. Braking system of a vehicle
3. Pumping bicycle/vehicle tyres with inflator
4. Using syrings to draw medicine
5. Pumping of water from a borehole
6. Hydraulic jack/press
7. Using straw

(i)

Surface tension is the propertey of a liquid that makes the surface behave as if it were a stretched elastic skin/membrane.

(ii)

Why the surface of water in a container is not flat but curved

The adhesive force between water molecules and the container is greater than the cohesive forces holding the water molecules together.

(i)

Effects of a force on a body

1. It changes direction of a moving body
2. It increases speed of a body/causes a body to accelerate
3. It decreases speed of a body/causes a body to decelerate
4. It causes a moving body to stop
5. It causes a stationary body to move
6. It causes deformation/changes the shape of a body

(ii)

Work done = Force x Distance

Work done = 250 N x 20 m
Work done = 5000 J

(i)

Types of forces

1. Force of gravity
2. Weight
3. Magnetic force
4. Electrostatic force
5. Frictional force
6. Centripetal force
7. Viscous force
8. Tensional/Elastic force
9. Adhesion
10. Cohesion
11. Centrifugal force

(ii)

1. Tensional/Elastic force
2. Force of gravity
3. Frictional force

(iii)

1. Tension/elastic force in the rubber band of the catapult pushed the stone
2. Force of gravity brought down the mango
3. Frictional force acts between the stone and the mango/between the leather of the catapult and the stone/between the palm and the stick of the catapult

i)

Surface tension is the property of a liquid which makes the surface behave as if it were a stretched elastic skin.

ii)

Household devices that make use of surface tension

1. Umbrellas
2. Raincoats
3. Tents
4. Canopies

iii)

Umbrellas/Raincoats/Tents/Canopies made of canvas do not leak because the surface tension of the water prevents the water from passing through the tiny holes in them

OR

In umbrellas/raincoats/tents/canopies made of canvas, water forms films like stretched elastic skin over each pore which prevents water from passing through.

(i)

Surface tension is the property of a liquid which makes the surface behave as if it were stretched elastic skin.

(ii)

One way in which surface tension can be useful to man

Umbrellas/raincoats/tents/canopies made of canvas do not leak because the surface tension prevents the water from passing through the tiny holes in them

OR

In umbrellas/raincoats/tents/canopies made of canvas, water forms films like stretched elastic skin over each pore which prevents water from passing through.

(i)

Viscosity is defined as the internal force that opposes the movement of liquid molecules.

(ii)

An experiment to compare the viscosities of two liquids A and B

1. Liquid A and B are both poured into two separate identical measuring cylinders to the same level
2. Two identical metal balls are dropped into each of the measuring cylinders and the time taken for each ball to reach the bottom/base of the cylinders of liquids A and B are recorded
3. The liquid in which the metal ball took a longer time to reach the base/bottom of the measuring cylinder is more viscous

(i)

Acceleratin = $\frac{\mathrm{Final\; velocity\; (v)\; -\; Initial\; velocity\; (u)}}{\mathrm{Time}}$

Final velocity = 150 ms^-1

Initial velocity = 100 ms^-1

Time = 10 s

Acceleratin = $\frac{\mathrm{150\; -\; 100}}{10}$ = 5 m^-2

(ii)

Force = Mass x Acceleration

Mass = 1000 kg

Acceleration = 5 ms^-2

Force = 1000 x 5 = 5000 N

(iii)

Momentum = Mass x Velocity

When the vehicle comes to a stop, the velocity is 0

Final momentum = 1000 x 0 = 0

(i)

Ways in which fluid pressure is applied in everyday activities

1. Water pumps
2. Car brakes
3. Drinking straw
4. Pumping tyre
5. Syringes
6. Siphon
7. Enema

(ii)

Substances that are an insulators

1.Dry wood
2. Air
3. Rubber
4. Plastic
5. Glass
6. Cloth

(i)

Area of a cuboid = Length x Breadth

Area = 5 cm x 10 cm = 50 cm²

(ii)

Pressure = $\frac{\mathrm{100\; N}}{\mathrm{50\; }{\mathrm{cm}}^2}$ = 2 Ncm^-2

α)

If 1 kgf = 10 N

0.75 kgf = $\frac{\mathrm{10\; N\; x\; 0.75\; kgf}}{\mathrm{1\; kgf}}$ = 10 N x 0.75 = 7.5 N

β)

If 1 kgf = 10 N

1.33 kgf = $\frac{\mathrm{10\; N\; x\; 1.33\; kgf}}{\mathrm{1\; kgf}}$ = 10 N x 1.33 = 13.3 N