Physics: Force
Physics Physics is the science of understanding forces A force is a push or pull. It has both direction and magnitude (strong/weak) General forces include gravity and friction Elastic forces include compression, tension, and torque
Gravity is a force that pulls towards the center of the Earth Gravity & Weight
Weight is a force that is a measure of gravity’s pull on an object Gravity & Weight Turkey Scale
To calculate the weight force of gravity’s pull on an object, multiply mass by gravity: 1.Convert mass in grams to kilograms (move the decimal to the left three places) 2.Multiply by gravity which on Earth is 9.8 Calculating Weight Force
The unit for all forces is the Newton (N) Named after Isaac Newton, the famous physicist Unit
If mass = 215 g force =.215 x 9.8 = = 2.1 N Examples: If mass = 1.2 g force =.0012 x 9.8 = = 0.01 N
Gravity increases with mass Understanding Gravity Gravity decreases with distance Large Mass More Gravity Small Mass Less Gravity
Think of gravity as massive objects creating warps in the fabric of space Understanding Gravity
Understanding Gravity – Newton vs Einstein
Two forces are always opposing motion: –Gravity –Friction Gravity & Friction Oppose Motion
Gravity is a force that slows upward and trajectory (on a path) motion by pulling objects towards the Earth Gravity Opposes Motion Gravity slows upward motion Gravity slows forward motion
Gravity pulls all objects to the Earth at the same rate no matter if they are dropped or shot from a gun Gravity Opposes Motion
Friction is a force that opposes motion between touching surfaces Motion Force Friction Force Friction Opposes Motion It is hard to walk without friction
The space shuttle and meteors (shooting stars) have air friction between their surface and our atmosphere Friction Opposes Motion
Friction creates heat and wears out objects Hip Replacement Friction Opposes Motion
Lubrication, such as oil and grease, help reduce friction Friction Opposes Motion
There are two basic types of friction: static and kinetic. Static friction is the stronger force of the two. Friction Opposes Motion
Static friction occurs before movement takes place - it resists movement. Motion Force Friction Force Friction Opposes Motion
Kinetic friction occurs during movement - it tries to slow or stop movement. Motion Force Friction Force Friction Opposes Motion
Example Question What two forces oppose the motion of this bike? Motion Force Friction Force
Elastic Forces Compression Forces come together from opposite directions (crushing a can) Don’t try this at home!
Forces applied in opposite directions (tug of war) Elastic Forces (continued) Tension
Elastic Forces (continued) T o rque A twisting force (the ‘O’ in torque)