Forces

Science mindmap- Forces, Pressure, Turning Effect of Forces

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Forces by Mind Map: Forces

1. Pressure

1.1. In everyday life

1.1.1. large pressure created at sharp point of a pin, allows it to pierce paper and wooden boards

1.1.1.1. small force produces large pressure on cutting edges, allows edges to cut through objects easily

1.1.1.1.1. spikes on soles of football shoes have small area, large pressure produced by the spikes increases shoe's grip on the ground

1.2. Factors

1.2.1. Force

1.2.1.1. can reduce pain in fingers by carrying fewer durians

1.2.1.1.1. smaller weight of fewer durians causes smaller force to be exerted on his hand

1.2.2. Area

1.2.2.1. can reduce pain in fingers by padding the handles with a thick cloth

1.2.2.1.1. handles now rest on a larger area

1.3. Definition

1.3.1. force acting per unit area

1.3.1.1. symbol: P

1.3.1.1.1. SI Unit: N/m² or Pa

1.4. Atmospheric pressure

1.4.1. pressure exerted by air in earth's atmosphere

1.4.2. when we drink liquid using a straw, we make use of atmospheric pressure to push water up into the tube

1.4.2.1. by sucking through the straw, we lower the air pressure in the straw

1.4.2.1.1. higher atmospheric pressure outside the straw pushes liquid up drinking straw

1.4.3. hold suction cups securely on kitchen and bathroom tiles, car windscreens

1.4.3.1. suction cup drops, because air enters it when it is not sealed completely, amount of air pressure in it matches atmospheric pressure

1.5. In liquids

1.5.1. submarines dive to great depths underwater

1.5.1.1. rigid metal bodies built to withstand high pressure deep underwater

1.5.1.1.1. if it dives beyond a certain depth, pressure may become too high and damage it

1.5.2. water is delivered to and stored in tanks at the top of most high-rise buildings

1.5.2.1. causes water in pipes below the tanks to be at high pressure and ensures that water flows to the units below

2. Turning effects of forces

2.1. Moment of a force

2.1.1. force can create a turning effect about a pivot

2.1.1.1. torque

2.1.2. product of force (F) and the perpendicular distance (d) from line of action of force to pivot

2.1.2.1. F x d∟

2.1.2.1.1. SI Unit: Nm (newton-metre)

2.1.3. Applications

2.1.3.1. Singapore Flyer

2.1.3.1.1. opening a lid using a screwdriver

2.1.3.2. levers

2.1.3.2.1. simple machine which turns about a fulcrum or pivot when a force called effort is applied to overcome another force called load

2.1.4. principle of moments states that when a body is in equilibrium, the sum of the clockwise moments about a pivot is equal to the sum of the anticlockwise moments about the same pivot

2.1.5. when a plank does not rotate about the pivot, pivot is stationary

2.1.5.1. upward force acting on pivot (normal contact force)

3. Definition

3.1. push or pull that one object exerts on another

4. Types

4.1. Normal Reaction force

4.1.1. push exerted by a surface on an object pressing on it

4.1.1.1. push is always perpendicular to the surface

4.2. Weight/Gravitational Force

4.2.1. gravitational pull of Earth on an object

4.2.1.1. force of attraction between two bodies

4.2.1.1.1. depends on mass of object being attracted, and mass of object attracting other objects

4.2.2. affects Earth, Moon and planets in Solar System

4.2.2.1. responsible for movement of high and low tides in harbours, ports and coastal areas

4.2.2.1.1. caused partly by moon’s gravity pulling on waters of the ocean

4.2.3. gravitational field, region in which a mass experiences gravitational force

4.2.3.1. gravitational field strength, gravitational force acting per unit mass on an object

4.2.3.1.1. SI Unit: N/kg

4.3. Friction

4.3.1. opposes or tends to oppose motion

4.3.1.1. exists between the surfaces of two objects in contact

4.3.1.1.1. at least one surface must be uneven

4.3.2. Negative effects

4.3.2.1. causes moving objects to slow down and come to a stop

4.3.2.1.1. causes things to heat up and wear out

4.3.3. How to reduce

4.3.3.1. ships and fishes have streamlined shapes to reduce water resistance

4.3.3.1.1. hovercraft ‘floats’ or hovers above water on a cushion of air to reduce friction between its base and water

4.4. Resistance/Viscous force

4.4.1. found in fluids such as oil or air

4.5. Tension

4.5.1. exerted by a stretched spring, string or rope on an object that is attached to it

4.6. Electrostatic force/Electric force

4.6.1. push or pull between electric charges

4.6.2. when handling plastic wrap, electrostatic forces cause the hairs on our arms and the dust on the table to be attracted to the plastic wrap

4.6.2.1. static electricity- electric charges that do not flow in an electric circuit

4.6.2.1.1. can attract and repel other static charges nearby

4.7. Magnetic force

4.7.1. push or pull between magnets or magnets on magnetic materials such as iron and steel

4.7.1.1. attraction and repulsion

4.7.1.1.1. act at a distance

4.7.2. Applications

4.7.2.1. separate magnetic materials from non-magnetic materials in waste recycling plants

4.7.2.1.1. make use of magnetic force of repulsion to lift a maglev train above its track when it is moving

5. Mass VS Weight

5.1. Mass

5.1.1. measure of amount of matter or substance in a body

5.1.1.1. SI Unit: kg

5.1.1.1.1. scalar (magnitude only)

5.2. Weight

5.2.1. measure of amount of gravitational force acting on a body

5.2.1.1. SI Unit: N

5.2.1.1.1. vector (magnitude and direction)

6. Effects

6.1. crash tests determine if cars meet the safety requirements

6.1.1. as car crashes into barrier, test dummies in the car measure the large forces acting on the driver and passengers

6.1.1.1. change the shape of a car and stop its motion

6.1.1.1.1. make the car begin to move from rest or move faster

6.2. change size and shape of objects

6.2.1. change state of rest of a body

6.2.1.1. change direction of moving objects

6.2.1.1.1. make moving objects go faster

7. Free Body Diagram

7.1. simple block diagrams with arrows to represent forces acting on a body

7.2. Weight

7.2.1. starts from centre of object

7.2.1.1. vertically downwards

7.3. Normal Reaction Force

7.3.1. starts from contact surface and cuts through the centre of the object

7.3.1.1. perpendicular to contact surface

7.3.1.1.1. upwards

7.4. Friction

7.4.1. lies on contact surface

7.4.1.1. opposite direction of motion/applied force