P15: Forces And Matter Flashcards
(18 cards)
How many forces are required to compress, bend or stretch an object?
More than one; it takes multiple forces (in different directions) to deform an object.
Explain the relationship between the force applied and the extension of an elastic object?
The extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.
What is meant by an inelastic (plastic) deformation?
• A deformation which results in the object being permanently changed
• The object doesn’t return to its original shape when the force is removed
What type of energy is stored in a spring when it is stretched?
Elastic potential energy.
What can extension be replaced with in the equation for spring force?
Compression.
Differentiate between elastic and inelastic distortion?
An elastic distortion is a temporary change. The object reverts to its original shape once the forces are removed. An inelastic distortion leads to a permanent change in shape. It is irreversible.
When is there a linear relationship between force and extension?
When an object is deforming elastically; when it has not yet reached the limit of proportionality.
When is there a nonlinear relationship between force and extension?
When the limit of proportionality has been exceeded, and the object is undergoing plastic deformation.
What is meant by the term ‘fluid’?
A liquid or a gas.
In any fluid, at what angle do the forces due to pressure act on a given surface?
At right angles (normal to) the surface.
Why does atmospheric pressure vary with the height above the earth’s surface?
The number of air molecules decreases the higher you go. This means that the weight of air above a point decreases, meaning the pressure also decreases.
True or False? The pressure in a fluid is determined by the fluid and the atmospheric pressure?
True
What direction does pressure act in?
All directions.
How does pressure in fluids increase with depth?
As the depth increases the mass of the liquid above the point also increases. This means that the force produced by that mass also increases. Since the force has increased whilst the area has remained constant, the pressure will increase.
Why does pressure in fluids increase with density?
As density increases there are more particles in a given volume of the liquid, hence the weight of the liquid is increased. This means that the force of liquid above a certain point is larger. Since the force has increased, the pressure must also increase.
Why are objects in a fluid subject to an upthrust?
• When an object is submerged in fluid, it experiences a higher pressure below it than it does on top of it.
• This leads to an upwards force called upthrust.
Why is the magnitude of the upthrust felt by an object?
Upthrust is equal to the weight of fluid displaced by the object.
How can you determine if an object will sink or float?
If the upthrust is greater than the weight of the object, it will float. If the weight is the greater force, it will sink.
