Forces Drawing Free Body Diagrams Remember force is
Forces Drawing Free Body Diagrams
Remember force is a vector § If a force acts at an angle it can be resolved into horizontal and vertical components. § To find the total froce acting on an object – draw the vector forces and add head to tail
Key forces § § § § Contact forces Friction Tension Support Air resistance Spring force Applied force § Forces that act at a § § § distance gravitationa; l Electrical magnetic
Weight force due to gravity § Any 2 objects have § § gravitational attraction between them because of their mass The force of the earth on a mass is significant. Fg = ma Gravity a=g = 9. 8 ms-2 Fg = mg
Friction force § A force which opposes motion § Air resistance is a friction force § Terminal velocity occurs when air resistance = force of gravity
Tension and support forces § Tension Forces occur in ropes and wires etc. § Support forces occur when objects rest on a surface because of Newton’s 3 rd law.
Free body diagrams § Draw a simple diagram of activity § Replace object with a dot § Draw force vectors out from the dot and label § To find resultant force, add vectors head to tail (if a closed loop occurs the net force is 0 and there will not be any acceleration.
The ollie It’s a matter of physics….
The forces of an ollie Just before the ollie there are 3 forces acting § Rider’s weight (red) § Board’s weight (black) § Ground support (blue) The forces are balanced so the speed is constant
Changing the forces to make an ollie Skater accelerates up by straightening legs and raising arms. Rear foot exerts a bigger force than front causing board to pivot on rear wheel
As the tail strikes the ground § The ground exerts a large upward force on the tail § The board bounces as a result § Board pivots around its center of mass
The board is now in the air § Skater now slides foot forward § Uses friction between foot and the rough deck to bring the board up even higher
Coming back down The skater § Pushes front foot down to raise the rear wheels and level out the board § Pulls up rear leg to get it out of the way of tail of the board
Maximum height § Board is now level at maximum height § Only force acting on board is gravity § Gravity also acts on the skater § Board and skater fall together at 10 ms-2
Whoa dude – physics is cool § Gravity wins § Skater bends legs to absorb the impact of landing § Our starting forces are acting again!
- Slides: 15