Forces

What is the equation for elastic potential energy?

elastic potential energy = 0.5 x spring constant x extension²

What is needed in order to change a shape?

• atleast two forces must be applied in different (but not necessarily opposite) directions

What does elastic mean?

• can go back to its original shape

What does inelastic mean?

• it cannot go back to its original shape when force is removed

What is the elastic limit?

• the furthest point it can be deformed while being able to return to its previous shape

• once past this point, deformation is inelastic

What is Hooke’s law?

• The force applied is directly proportional to the extension

• true until the elastic limit (limit of proportionality)

• F=ke

Describe a method for investigating springs

Secure a clamp stand to the bench using a G-clamp or a large mass on the base.

Use bosses to attach two clamps to the clamp stand.

Attach the spring to the top clamp and a ruler to the bottom clamp.

Adjust the ruler so that it is vertical and with its zero level with the top of the spring.

Record 0N and an extension of 0cm in your table.

Hang a 100 g slotted mass carrier - weight 1N - from the spring. Measure the new

length of the spring and calculate extension. Record extension in your table.

Repeat step 6, increasing the load by 1N each time.

Plot a graph of Force (N) against extension (cm)

Find the spring constant using F=ke (remember to convert from cm into m)-

What is a moment?

• turning effect of a force

What is the equation that links moment,force and perpendicular distance?

• Moment (Nm) = Force(N) x Distance (m)

What does it mean for an object to be balanced?

• total clockwise moment = total anticlockwise moment

How do levers make it easier to do work?

• by increasing the distance from the pivot at which the force is applied, less force is needed to get the same moment

What is a force multiplier?

• reduce the amount of force needed to get the same moment by increasing the distance

• e.g long sticks make it easier to lift heavy objects off the ground

• e.g wheelbarrows let you move a load that would normally be too heavy to lift

• e.g scissors let you cut through objects that would be too tough to get through with just a knife

What are gears?

• circular discs with ‘teeth’ around the edges

• teeth interlock, turning one causes another to turn in the opposite direction

• used to transmit the rotation effect of a force

• e.g bicycles use gears to transmit turning effect of pedals to back wheel