Physics chp4

Explain the difference between mass and weight

Weight measured in Newtons, magnitude is variable, depends on location where as mass is measured in Kg and is constant for a specific object anywhere in the universe

weight = mass x gfs

Define centre of gravity

An imaginary point at which the entire weight of an object seems to act

How can you find the centre of gravity of a 3D shape?

Freely suspend card from clamp stand and hang a plumb line

Draw line along plumb line and repeat for 2 more suspensions

Centre of gravity where lines intersect

What are the two most important factors that affect magnitude of drag?

Speed and cross-sectional area of the object

Describe how the forces on an object change as it falls through a fluid

At the instant it starts to fall: total force = weight of the object and acceleration = g

As the object falls its speed increases which in turn increases the magnitude of the opposing drag force and decreases the instantaneous acceleration

Eventually the object reaches terminal velocity, drag force is equal and opposite to weight, acceleration is zero and speed is constant

Define drag

The frictional force experienced by an object travelling through a fluid

Define a Newton

The force needed to accelerate a body weighing one kilogram by one metre per second per second

What is the principal of moments?

For a body in rotational equilibrium: sum of the clockwise moments = sum of the anticlockwise moments

Define couple

Two forces that are equal in magnitude but that act in opposite directions to each other, have different lines of action.

Doesn’t cause any resultant linear force but does produce a turning force (torque)

Define torque

The turning effect due to a couple

How can you calculate torque?

Torque = size of one of the forces x perpendicular distance between forces