Topic 9- forces and their effects Flashcards
What are contact forces?
forces that require touch between objects in order for the force to act
What is the non-contact forces?
Forces that act at a distance. e.g. gravitational, electrostatic and magnetic fields
What causes the gravitational attraction between objects (like the earth and sun)
their gravitational potential strengths interacting
What causes attraction and repulsion between magnetic objects?
Interacting magnetic fields
What causes attraction and repulsion between electrical charges?
Interactions between their electric fields (electrostatic forces)
What does a free body force diagram show?
An isolated body and all of the forces acting on it
What shouldnt a free body force diagram include?
The forces it exerts on the rest of the world
Objects in equilibrium have a resultant force of ….. and are either ……. or moving at a ………………?
- Zero
- Stationary
- Steady speed
Which direction does normal contact force act?
Upwards
What is Newton’s third law?
Whenever two objects interact, both objects feel an equal but opposite force
Describe how you use scale drawings?
- Draw all forces acting on an object to scale, tip to tail
- 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 length of resultant force. (cm - N)
What is a moment?
The turning effect of a force
What would the force on a spanner cause?
A turning effect or moment on the nut
What is the formula to calculate the size of a moment
moment of a force = force *distance
How could you get the maximum moment?
Push at right angles to the object to get the largest distance
What is the principle for an object that is in equilibrium (moments)
The sum of anticlockwise moments = the sum of clockwise moments
Describe how levers work and why theyre useful
Levers transfer the turning effect of a force - push one end of a lever down and the rotation around the pivot causes the other end to rise. Levers make it easier to do work as they increase the distance from the pivot at which the force is applied - the longer the lever, the smaller the force needed to give the same moment
What would happen to a moment with a large gear that has 16 teeth and a smaller gear that has 8 teeth
The ratio of teeth would be 2:1 and therefore the moments would also be 2:1..
Why are gears often lubricated?
Lubrication reduces friction and unwanted energy transfers. Therefore, they improve the efficiency of the machines
