forces and their interactions

scalar and vector quantities, contact and non contact forces, gravity, resultant forces, work done & energy transfer, forces & elasticity

what is a scalar quantity

a quantity that only has a magnitude

what is a vector quantity

a quantity that has a magnitude and direction

what are some examples of scalar qualities

energy

temperature

mass

speed

what are some examples of vector quantities

force

displacement

velocity

acceleration

momentum

what is velocity

speed in a defined direction

what is displacement

distance travelled in a defined direction

what is a force?

a push or pull

how do you draw vectors

the length of the line is the magnitude and the direction is the direction

what are 3 things that force can do?

• change the shape of an object

• change the speed of an object

• change the direction an object is travelling

what are contact forces?

force that is exerted when two objects touch

what is a non contact force

force that can be exerted without two objects physically touching

examples of contact forces

• friction

• air resistance

• tension

• normal contact force

examples of non-contact forces

• gravity

• electrostatic forces

• magnetic forces

the size of forces: a) the pull of gravity on a fly

b) the pull of gravity on an apple

c) the force required to squash an egg

d) the tension in a rope towing a car

a) 0.001N

b) 1N

c) 50N

d) 1000N

what is gravitational force (gravity)

the force of attraction between masses

what is the gravity on earth?

9.8N/kg

what is weight

the force acting on an object due to gravity

what is the formula for weight

weight (N) = mass (kg) x gravitational friend strength (N/kg)

what is the relationship between mass and weight?

they are directly proportional. when mass increases weight increases

what are resultant forces

a number of forces acting on a single object, as a single force

what is work done?

when a force moves an object through a distance

what is the formula for work done

work done (J) = force (N) x distance moved in the direction of the force (m)

what is one joule equivalent to

one newton-meter

what happens when work is done?

energy is transferred

were is energy transferred when you push start a car

to the kinetic energy of the car

does a force always do work?

no

what is an example for work not being done

if you are pushing an object, but not in the direction of movement

what is it called when an object returns to its original shape after being stretched

elastic deformation

what is it called when an object doesn’t return back to its original shape after being stretched

inelastic deformation

what is extension

the difference between the stretched and unstretched lengths of a spring

what is the relation between force applied and deformation?

small force → an object springs back to its original shape

large force → an object changes shape permanently

what is the formula for spring extension

force (N) = spring constant (N/m) x extension (m)

what is the spring constant

measures how stiff a spring is. the larger the spring constant the more stiff the spring is

what is the formula for finding out the work done in stretching/compressing a spring

elastic potential energy (J) = ½ x spring constant (N/m) x (extension)² (m)²

how would you investigate the relationship between force and extension of a spring?

• set up a clamp with a millimetre ruler clamped to the stand.

• attach a spring to the top of the clamp

• add masses to the bottom of the spring and allow the spring to come to rest. record the mass and the new length of the spring. the extension is the change in length