Forces
Summary
- Newton's first law of motion (also known as the law of inertia) states that…
- an object at rest tends to remain at rest and…
- an object in motion tends to continue moving with constant velocity…
- unless acted upon by a net external force.
- In general, inertia is resistance to change.
In mechanics, inertia is resistance to change in velocity (resitance to acceleration).- Moving objects do not need to be pushed to continue moving.
- A constant velocity of zero (at rest for an extended period of time) is one type of constant velocity.
- In general, a force is an interaction that causes a change.
In mechanics, a force is an interaction that causes a change in velocity (an interaction that causes acceleration).- Forces must be external to cause a change. (Objects cannot push themselves.)
- When more than one force is present, it is the net force (combination) that matters.
- Supplementary Materials
- Summary as a concept map
- Original statement in Latin from Newton's Principia with English translation
| name/symbols | when/where | direction | |
|---|---|---|---|
| weight | W, Fg | due to gravity | down |
| normal | N, Fn | surfaces in contact | normal to surface |
| friction | f, Ff | surfaces in contact | tangent to surface |
| tension | T, Ft | strings, ropes, cables, etc | along the axis |
| elasticity | Fe, Fs | springs, rubber bands, etc. | along the axis |
| buoyancy | B, Fb | immersed in a fluid | up |
| drag | R, D, Fd | moving through a fluid | opposite velocity of object |
| lift | L, Fℓ | moving through a fluid | perpendicular to flow* |
| thrust | T, Ft | pushing a fluid | opposite velocity of fluid |