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Flashcards in P5: Forces Deck (85)
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What do vector quantities have?

Magnitude and direction.


What do scalar quantities have?

Just magnitude.


Give 5 examples of vector quantities.

Force, volocity, displacement, acceleration, momentum.


Give 5 examples of scalar quantities.

Speed, distance, mass, temperature, time.


What are the two categories of forces?

Contact and non-contact.


What is gravity?

The force of attraction between masses.


How are weight and mass different?

Mass is a measure of the amount of matter in an object, so remains the same everywhere. Weight is a force which acts on an object due to gravity. A measurement of weight could change with location.


What can be used to measure mass?

A mass balance (balancing scales).


What can be used to measure weight?

A calibrated spring balance (newtonmeter).


Mass and weight are directly proportional. What formula links them?

Weight = mass x gravitational field strength


What is the unit for weight?

Newtons (N).


What is the unit for mass?



What is the unit for gravitational field strength?



When a force moves an object through a distance...

...work is done on the object.


Work done =

energy transferred (and force x distance).


What equation can be used to find work done?

Work done = force x distance


If all the forces acting on an object combine to give a resultant force of 0, it is in __.



What is elastic deformation?

Where an object returns to its prior shape after the force deforming it is removed.


What is inelastic deformation?

Where an object doesn't return to its prior shape after the force deforming it is removed.


What is meant by the limit of proportionality (in the context of springs)?

The point where a spring's extension stops being proportional to the force applied to it. A plotted graph would become non-linear at this point.


What equation is used to find the force applied to a spring when stretching/compressing it?

F = ke (force = spring constant [N/m] x extension [m])


How can you work out the energy in a spring's elastic potential store from a force-extension graph?

Use the given equation E = 1/2ke2.



Plan an investigation to show the relationship between force and extension for a spring.

  • Use a stand to suspend a spring. Clamp a mm ruler in line with the spring.
  • Record the natural length of the spring, taking the reading at eye level.
  • Hang a mass on the spring and measure its length. Calculate the extension by substracting the initial length.
  • Repeat this process, adding one identical mass each time, until you have 6 measurements.
  • If one extension is larger than the previous, the limit of proportionality has been succeeded. You'll need to repeat the experiment, with a new spring and lighter masses.
  • Calculate the force exerted on the spring per mass (weight = mass x gravitational field strength).
  • Plot force exerted on the spring (x axis) against spring extension. You should see a directly proportional / linear relationship.
  • You could find the spring constant using the equation F = ke.


What is the moment (or torque) of a force?

Known as the turning effect of a force, it is the rotational equivalent of linear force, i.e. a twisting force.


What equation is used to find the moment of a force?

M = Fd (moment [Nm] = force x perpendicular distance from pivot to line of action of force)


What is the unit for moment?

Newtonmeters (Nm)


How would you maximise the moment of a force?

1) Making the force's direction perpendicular to the lever (assuming it's straight). 2) Increasing the length of the lever.


When is an object on a pivot balanced (doesn't turn)?

When the total anticlockwise moment = total clockwise moment.


What are gears used for and how do they work?

• Used to transmit the rotational effect of a force.

• Turning one causes another to turn in the opposite direction, changing the rotational direction.

• Transmitting a force to a larger gear causes a bigger moment, but this gear will turn slower.


What is pressure?

Force per unit area.