Chapter 8 - Modelling in Mechanics Flashcards
What is friction?
✯ A force which opposes motion on rough surfaces.
What is tension?
✯ When an object is pulled along a string, the force acting on the object is the tension in the string.
What is air resistance?
✯ Air resistance, on the other hand, opposes the motion of an object through the air, regardless of its direction.
What is buoyancy?
✯ Buoyancy is an upward force that opposes weight, allowing objects to float or rise in a fluid.
What is thrust/compression?
✯ The force that acts on an object, when being pushed along using a light rod.
What is a vector?
✯ Vector – A quantity which has both magnitude and direction. Motion in a straight line (1-dimensional motion) can be positive or negative.
What is a scalar?
✯ Scalar – A quantity which has magnitude only. THEY ARE ALWAYS POSITIVE.
Modelling Assumptions
What assumptions are made when the model is a particle?
✯ The mass of an object concentrated at a single point.
✯ Ignore the air resistance and rotational forces.
What assumptions are made when the model is a rod?
✯ Mass is concentrated along a line.
✯ No thickness.
✯ Rigid.
What assumptions are made when the model is a lamina?
✯ Mass is distributed along a flat surface.
What assumptions are made when the model is a uniform body?
✯ Mass is concentrated at the centre of the body.
What assumptions are made when the model is a light object?
✯ Treat the object as having zero mass.
What assumptions are made when the model uses a string once?
✯ Tension is the same at both ends of a light string.
What assumptions are made when the model is a light inextensible string?
✯ Connected particles will have the same acceleration
What assumptions are made when the model is a smooth surface vs rough surface?
✯ Smooth Surface: No friction is present.
✯ Rough Surface - Objects in contact with this surface experience a frictional force.
What assumptions are made when the model is a wire?
✯ One dimensional.
What assumptions are made when the model is a smooth and light pulley?
✯ Pulley has no mass.
✯ Tension is the same in either side of the pulley.
What assumptions are made when the model is a bead?
✯ Tension is the same on either side of the bead.
✯ Move freely along a string or wire.
What assumptions are made when the model is a peg?
✯ Dimensionless and fixed.
What assumptions are made when the model uses air resistance?
✯ Usually, we neglect air resistance.
✯ Assuming air resistance is negligible means we can ignore the frictional effects of the air on the object.
What assumptions are made when the model is a acting under gravity?
✯ Acceleration = 9.8ms^-2
✯ Gravity acts downwards.
