Motion and Force in Physics

Study Notes

A force is a push or pull upon an object resulting from its interaction with another object
Force exists only as a result of some interaction
Force does not always involve effort by living beings like humans or animals
Force can also be due to natural causes

Change in the state of motion: change in speed or direction of motion
Change in size/shape of an object
Force can make an object move from rest, change the speed of a moving object, or change the direction of motion of an object

Greater is the applied force, greater is the change in the speed of the object
The mass of an object and the value of the change in its speed (in a given time) determine the magnitude of the force needed

Unbalanced forces, acting in the same direction, combine by addition
Unbalanced forces, acting in mutually opposite directions, combine by subtraction
The resultant (net) of unbalanced forces is always non-zero

Equal and opposite forces (balanced forces) do not change the state of rest or motion of an object
They may cause a change in the size and/or shape of the object

Contact forces: result from direct physical contact between two bodies (e.g. muscular force, frictional force)
Non-contact forces ('action at a distance' forces): can cause their effects even when the two interacting bodies are not in direct physical contact with each other (e.g. gravitational force, magnetic force)

Muscular force: caused by the action of muscles in our body
Frictional force: causes a ball rolling along the ground to come to rest
Frictional force depends on the nature of the two surfaces in contact
The direction of the frictional force is usually opposite to the direction of motion of the object### Gravitational Force
Causes objects to fall towards the ground, such as a thrown ball or ripe fruit
A universal force that affects everything with mass or energy

Causes magnets to attract objects made of iron
Like poles of two magnets repel each other, while unlike poles attract each other
Can exert a force on another magnet without physical contact

Always occur in pairs between two objects
The force exerted by one object on another is equal and opposite to the force exerted by the second object on the first

Occurs between two charged bodies, causing them to attract or repel each other
Glass rods become positively charged when rubbed with silk cloth, while ebonite rods become negatively charged when rubbed with wool
The attraction or repulsion between charged rods is due to the electric force between them