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