Download - Physics Topic 2
Physics Topic 2
Mechanics
• Distance – total length of the path travelled• Displacement – change in position from initial
to final
• Speed – distance travelled over time (scalar)• Velocity – DISPLACEMENT over time (vector)
Position vs. Time Graphs
Acceleration
• Acceleration – change in velocity over time
Velocity vs. Time Graphs
Slope is Acceleration!!!Area under curve is Distance!!!
Practice Problems
Free Fall
• When the only force acting upon an object isgravity.
• Acceleration due to gravity, g = 9.81 m/s2
Free Falltime (s) acceleration (m/s2) velocity (m/s) distance (m)
0 9.81 0 01 9.81 9.81 4.9052 9.81 19.62 19.623 9.81 29.43 44.1454 9.81 39.24 78.485 9.81 49.05 122.6256 9.81 58.86 176.587 9.81 68.67 240.3458 9.81 78.48 313.929 9.81 88.29 397.305
10 9.81 98.1 490.5
Free Fall in Vacuum
Forces• When two or more forces act on the same
object at the same time they are calledCONCURRENT FORCES.
• RESULTANT FORCE = the combined effect ofthe concurrent forces– Greatest when angle between forces = 0– Least when angle between forces = 180
• Resultant force show direction of movement
Add TheseForces
SubtractThese Forces
But what if the angle isn’t 0 or 180?
Solving with Weird Angles
1. Split up vectors into x and y components
2. Use Pythagorean theorem to find resultant
How do I find this angle?
tan θ = opp / adjθ = tan-1(opp/adj)θ = tan-1(300/400)θ = tan-1(0.75)θ = 36.869898°θ = ~37°
Newton’s 3 Laws of Motion
• Newton’s 1st Law– An object maintains a constant velocity unless
acted upon by an unbalanced force.
• AKA Law of inertia (resistance of an object tochange its position)
• Newton’s 2nd LawF = m(a)
• Newton’s 3rd Law– When one object exerts a force on a second
object, the second object exerts a force on thefirst that is equal in magnitude an opposite indirection.
2-D Motion & Trajectories
How to Solve Them
• SPLIT TRAJECTORIES INTO X-COMPONENTSAND Y-COMPONENTS.
Projectile Fired Horizontally• Initial y velocity = 0• Acceleration in y = g• Acceleration in x = 0• Time to hit ground is the sameas if it had just been dropped
Projectiles Fired at an Angle
Split The Problem in Half
• What happens half-way through theprojectile’s trajectory?
• Acceleration in the x =• Acceleration in the y =• Initial Velocity in x =• Initial Velocity in y =• Velocity in y at half-time =
0-9.81
V cos (θ)V sin (θ)
0
Greatest Range
Centripetal Force• Force needed to keep an object moving in a
circular path.
centripetal acceleration
Gravity• Everything with mass exerts a gravitational
force• Everything in this universe is gravitationally
attracted to everything else.• Weight = force of gravity on a planet
Friction• Friction – force that opposes motion• Normal Force – force pressing two contacting
surfaces together
Static and Kinetic Friction• Static friction must be overcome to make an
object move• Kinetic friction exists when the object is
moving
Inclined Plane
Momentum and Impulse
Conservation of Momentum
m1v1 = m2v2
What if they stick together?
m1v1 + m2v2 = (m1 + m2)vnew