JUST+FORCES

IGCSE PHYSICS > FORCES AND MOTION > FORCES. MOVEMENT AND SHAPE

 * ~ 1 FORCES ||~ 2 ELECTRICITY ||~ 3 WAVES ||~ 4 ENERGY ||~ 5 SLG ||~ 6 MAGNETISM ||~ 7 RADIOACTIVITY ||

Definition Types Vectors || FORCES CAUSE MOVEMENT Friction F=ma Terminal velocity || FORCES CHANGE MOMENTUM Momentum Car safety Newton's 3rd law || FORCES CAUSE TURNING Moments Centre of Gravity Beam on trestles || FORCES CHANGE SHAPES Stretching ||
 * JUST FORCES

see the Just Forces presentation at the bottom of the page!
1.8 express a force as a push or pull of one body on another. FORCE - Push or a pull on an object. It will accelerate an object or change its shape or size. A force is a vector quantity. It can also be a stretch, squash, bend, twist, turn 1.9 identify various types of force (eg gravitational, electrostatic etc)

TYPES OF FORCES

Non-contact - electrostatic, gravitational, magnetic

Contact - reaction; thrust; drag/ air resistance/ friction; lift; tension



1.10 distinguish between vector and scalar quantities. VECTOR: A quantity with both magnitude and direction. SCALAR: A quantity with only a magnitude.

ACTIVITY: Which quantities are vectors and which scalars? 1.11 appreciate the vector nature of a force 1.12 add forces that act along a line. ADDING FORCES ALONG A LINE: They are added like directed numbers taking into account positive or negative direction.

[|VECTOR ADDITION IN 2D] media type="custom" key="10695504" THIS PHET SIMULATION SHOWS HOW VECTORS CAN BE ADDED IN 2 DIMENSIONS (The Parallelogram Rule is not needed for IGCSE). Example: Add forces of 23 N east, 10 N west and 4 N east and illustrate. RESULTANT FORCE = 17 N east EXERCISE: Use the vector simulation at PHET to illustrate the following sums of vectors in one dimension (see example above): 1 20 N east plus 15 N east 2 12 km east plus 16 km west 3 12 N up plus 40 N down 4 300 m north plus 100 m south plus 250 m south 5 35 m/s to the left plus 8 m/s to right 6 A weight of 360 N pulled upwards with a force of 500 N 7 A car travelling forward at 105 km/h into a headwind of 27 km/h 8 A tug of war team pulling towards Shanghai with a force of 1500 N against a force of 1450 N

ACTIVITY: Find FIVE photos of moving and static objects and label them with forces arrows (there are several at the top of the page). Try to give them correct sizes and directions. A force is always the effect of one body on another one. 1 First show the weight of the object. 2 Show all the forces of things which are in contact. 3 Show any non-contact forces (magnetism or electrostatic)

Examples of types of force: Non-contact - electrostatic, gravitational, magnetic Contact - reaction; thrust; drag/ air resistance/ friction; lift; tension

EXTENSION: Use the Vector Addition simulation to explore the addition of forces in 2 dimensions. Look up the parallelogram rule.

EXTENSION 2: How big are these forces in newtons? Estimate or research them.
 * 1) Push of air of a square metre of earth
 * 2) Force of a nutcracker on a nut
 * 3) Gravitational force of the Sun on the Earth
 * 4) Force of an automobile braking
 * 5) Thrust of Saturn V rocket engines
 * 6) Air resistance on you when you are walking
 * 7) Force of a proton on an electron in a hydrogen

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