Forces Flashcards
What does a force-extension graph for rubber look like?
A curve of increasing gradient followed by a curve of decreasing gradient
How do I know if an object obeys Hooke’s Law from a table of data?
There is a constant increase in the extension of the object as I increase the force.
How do I know if an object obeys Hooke’s Law from a graph?
A straight line THROUGH THE ORIGIN.
What is Hooke’s Law?
Force is proportional to extension up to the elastic limit
What is the elastic limit?
The MAXIMUM force which, WHEN RELEASED, will cause the object to return to its original shape.
What does the word elastic mean?
When force is released the object returns to its original shape.
What does the word plastic mean?
When force is released, the object does not return to its original shape.
What does the term “terminal velocity” mean?
The constant speed an object arrives at when the driving force (usually weight) is equal and opposite to the frictional forces on the object.
Explain how an object can reach terminal velocity when falling.
The object starts at rest. The net force is due to weight downwards, so it accelerates downwards at 9.81 m/s2. As the object accelerates, it gains speed. Air resistance is proportional to speed squared, so as it gains speed, friction increases. Friction acts in the opposite direction to weight, so it acts to reduce the net force, so the acceleration decreases. Eventually, the friction is large enough so that it is equal but opposite to the weight. The forces are balanced. This means the net force is zero, and by Newton’s First Law it moves at constant speed. This constant speed is terminal velocity.
What does the term “balanced forces” mean?
Two forces that act in opposite directions that are equal in size.
What does the term “unbalanced force” mean?
Net force.
What is an object’s centre of gravity?
The location on an object where the weight acts.
