FORCES+AND+DYNAMICS

IB Physics > Mechanics
 * 1 Measure || 2 Mech || 3 Therm || 4 Waves || 5 Electric || 6 Fields || 7 Atomic || 8 EPCC || 9 MIF || 10 Therm AHL || 11 Wave Phen || 12 EMI || 13 QNP || 14 Digital || OPT || PRAC || REVISE ||


 * KINEMATICS || FORCES AND DYNAMICS || WORK, ENERGY AND POWER || UNIFORM CIRCULAR MOTION ||

FORCES AND DYNAMICS
Calculate the weight of a body using the expression W=mg. WEIGHT - The force of gravity on a body. W = mg, where W is weight/ N; m is mass/ kg; g is gravitational field strength/ Nkg -1. On Earth, g = 9.81 Nkg -1 Identify the forces acting on an object and draw free-body diagrams representing the forces acting. Each force should be labelled by name or given a commonly accepted symbol. Vectors should have lengths approximately proportional to their magnitudes. See sub-topic 1.3.

FREE-BODY DIAGRAM: Shows all of the forces acting ON an object. [|Free body diagram questions.doc]
 * 1) its weight acting vertically from the centre of mass
 * 2) all forces where it is contact with other objects
 * 3) any magnetic or electrostatic forces

FRICTION: The force which opposes motion when one surface moves over another. It is caused by the roughness of the surfaces. NORMAL REACTION: Two objects in contact each exert a force on the other which is perpendicular to the surface. TENSION: A force produced in a body when opposing forces are stretching it. The opposite is a compression force when two forces are squashing a body. UPTHRUST: An upward force on a body which is immersed in a fluid (liquid or gas). LIFT: An upward force on the wing of an aircraft due to the air flowing around it.

Determine the resultant force in different situations.

State Newton’s first law of motion. NEWTON’S FIRST LAW OF MOTION: A body continues to maintain its state of rest or of uniform motion in a straight line unless acted upon by an external unbalanced force.

INERTIA: The property of matter which makes it resist acceleration.

Describe examples of Newton’s first law.

State the condition for translational equilibrium.

TRANSLATIONAL EQUILIBRIUM: When the net force on an object is zero in all directions (ie no linear acceleration).

Solve problems involving translational equilibrium.

State Newton’s second law of motion.

Students should be familiar with the law expressed as: F = ma and F = Δp/Δt



NEWTON’S SECOND LAW OF MOTION: ∑F = ma The rate of change of momentum of an object is proportional to the applied force and takes place in the direction in which the force acts. Solve problems involving Newton’s second law. Define linear momentum and impulse.

IMPULSE: The change in momentum. A vector. Unit is Ns LINEAR MOMENTUM: the product of mass and velocity. It is a vector measured in kgms-1

Determine the impulse due to a time-varying force by interpreting a force–time graph.





State the law of conservation of linear momentum.

LAW OF CONSERVATION OF LINEAR MOMENTUM: The momentum of an isolated system remains constant (ie when no external forces are acting). Or, in any isolated system, the change in momentum is zero.

Solve problems involving momentum and impulse.

State Newton’s third law of motion. NEWTON’S THIRD LAW OF MOTION: Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction.

Discuss examples of Newton’s third law. Students should understand that when two bodies A and B interact, the force that A exerts on B is equal and opposite to the force that B exerts on A.

RESOURCES [|ASTRONOMY CAST PODCAST ON GRAVITY]