4.5.1.4 Resultant forces + 4.5.2 Work done and energy transfer

what is a resultant force

the overall force on a point or object

if you have a number of forces acting on a single point, you can replace them with a single force

this single force is called a resultant force

what does a free body diagram show

all the forces acting on an object

what happened to work if a resultant force moves an object

work is done

equation for work done, force and distance

W= Fs

\
work done (j)

Force (N)

distance (moved along the line of action of force(m))

joules and newton-metre

1 joule = 1 newton-metre

frictional forces

Work done against the frictional forces acting on an object causes a rise in the temperature of the object.

when you push something along a rough surface you are doing work against frictional forces. Energy is being transferred to the kinetic energy store of the object because it starts moving, but some is also being transferred to thermal energy stores due to the friction. Causes the overall temperature of the object to increases

using sale drawings to find resultant forces

1. draw all the forces acting Onan object, to scale
2. draw a straight line from the start of the first force to the end of the last force- this is the resultant force
3. measure the length of the resultant force on the diagram to find the magnitude and the angle to end the direction of the force

Pythagorus rule

a + b = c²

F²= (Fcos∅)² + (Fsin∅)²

what do balanced forces mean

that an object has an equilibrium

if all of the forces acting on an object combine to give a resultant force of 0