IGCSE Physics Revision Notes Effects of forces

CORE:

• Know that forces may produce changes in the size and shape of an object
• Sketch, plot and interpret load–extension graphs for an elastic solid and describe the associated experimental procedures
•  Determine the resultant of two or more forces acting along the same straight line
• Know that an object either remains at rest or continues in a straight line at constant speed unless acted on by a resultant force
• State that a resultant force may change the velocity of an object by changing its direction of motion or its speed
• Describe solid friction as the force between two surfaces that may impede motion and produce heating
•  Know that friction (drag) acts on an object moving through a liquid
•  Know that friction (drag) acts on an object moving through a gas (e.g. air resistance)

EXTENDED:/ SUPPLEMENT:

• Define the spring constant as force per unit extension; recall and use the equation k = F /x
• Define and use the term ‘limit of proportionality’ for a load–extension graph and identify this point on the graph (an understanding of the elastic limit is not required)
•  Recall and use the equation F = ma and know that the force and the acceleration are in the same direction
•  Describe, qualitatively, motion in a circular path due to a force perpendicular to the motion as:
• (a) speed increases if force increases, with mass and radius constant
• (b) radius decreases if force increases, with mass and speed constant
• (c) an increased mass requires an increased force to keep speed and radius constant (F = mv² /r is not required)

1.5.2 Turning effect of forces

CORE OBJECTIVES:

• Describe the moment of a force as a measure of its turning effect and give everyday examples
•  Define the moment of a force as moment = force × perpendicular distance from the pivot; recall and use this equation
•  Apply the principle of moments to situations with one force each side of the pivot, including balancing of a beam 
• State that, when there is no resultant force and no resultant moment, an object is in equilibrium

EXTENDED/SUPPLEMENT OBJECTIVES:

• Apply the principle of moments to other situations, including those with more than one force each side of the pivot
•  Describe an experiment to demonstrate that there is no resultant moment on an object in equilibrium

1.5.3 Centre of gravity

CORE OBJECTIVES:

• State what is meant by centre of gravity
• Describe an experiment to determine the position of the centre of gravity of an irregularly shaped plane lamina
•  Describe, qualitatively, the effect of the position of the centre of gravity on the stability of simple objects

SUPPLEMENT  OBJECTIVES:

[NONE]