Physics Flashcards
Newton’s 1st Law (Law of inertia)
A object continues in a state of rest or motion at constant velocity, unless compelled to change that state by a net force.
Inertia: ability of an object to resist a change to its velocity
Mass: measure of object’s inertia
Force
Any influence capable of creating a mass to accelerate
A vector
Measured in Newtons (kg x m/s^2)
Center of Mass Equation
Cmass= (r1m1 + r2m2 + r3m3 + …)/mtotal
r: displacement vector between a reference point on each mass.
Step 1: choose reference point, “origin of coordinates” from which to measure each displacement vector.
Center of gravity
At the center of mass
Center of buoyancy
Center of mass of the fluid displaced by the submerged object
Newton’s 2nd Law
Fnet= ma
Constant force will not an cause an object to accelerate faster and faster, it will cause a constant (non-changing) acceleration.
Cannot accelerate a ball horizontally across a room by throwing it
Newton’s Third Law
Whenever an object exerts a force (via contact or field) on a second object, the second object always exerts an equal and opposite force on the first object.
Velocity vs speed
Velocity is a vector
Speed is a scalar
Velocity is change in displacement over change in time
Speed is change in distance over change in time
Constant velocity (or constant velocity)
Treat the same if and only if the distance traveled is on a straight line.
Constant velocity and constant speed THINK:
- no acceleration
- No note force
- all forces sum to zero
- no change in direction
- the object is in equilibrium
Acceleration
Change in velocity over change in time
Vector
If there is no net force, there can NEVER be an acceleration, however, there CAN be a force and no acceleration (forces cancel out)
Linear motion graphs:
How to interpret them
- What does the slope represent?
- Is this slope positive or negative? What does the sign of the slope tell you?
- Is the slope constant (straight line) or non constant (curved line)? What does the observation tell you?
- What value is on the y-axis?
- Is the y-value (+) or (-) (are you above or below the x-axis)? What does that tell you?
- Do you expect the value on the y-axis to be large or small at t=0?
Average velocity
v (ave)= (v1+v2)/2
Distance (or height) traveled
Distance= rate x time
Projectiles
Range: horizontal distance traveled
Range= vx x time
- Horizontal velocity NEVER changes (ignoring air resistance)
- Horizontal acceleration =0 always
- Vertical acceleration always = 10 m/s^2 downward
- Vertical behavior is exactly symmetrical (upward trip identical to downward trip)
- Time in air depends on the vertical component of the velocity only
- Range depends on both vertical and horizontal compounds
- Time is always the same for both x and y components of the motion
X= 1/2at^2
Find distance
v=(2gh)^0.5 or v=(2ax)^0.5
Use when asked for final velocity given drop height
tair= 2v/g
Used ONLY to calculate “round trip” times, or, total time in the air
Variable V must be vertical component of vi
Air resistance characteristics
Factors that affect magnitude of air resistance
- Cross Section Area: greater CSA impacting air, more air resistance
- Shape: less aerodynamic, more air resistance
- Velocity: greater velocity, more air resistance
Always assume AR is ignored! Unless specified.
At terminal velocity,
Fair= mg
Forces of gravity and air resistance are now balanced
Friction (kinetic and static)
Static: Ff= UsFn or Ff= Usmgcosx
Kinetic: Ff= UkFn or Ff= Ukmgcosx
Max static friction: friction created before an object begins to slide will always remain equal to the net applied force which the friction is opposing
Inclined planes
F=mgsinx (force down inclined plane, = to surface)
F=mgcosx (normal force on an inclined plane)
vf=(2gh)^0.5 (velocity of a particle at bottom of inclined plane)
Acceleration on projectile
Always 10 m/s^2 (downard) during entire flight. Doesn’t change at max height.
Acceleration NEVER becomes 0, even at the exact peak
VELOCITY does reach an instantaneous zero
Velocity vector is the only vector that changes direction during projectile motion
Vectors
Magnitude and direction Examples: Velocity Displacement Acceleration Force Weight Electric field Magnetic field Momentum Impulse Torque
Scalars
Magnitude only Examples: Mass Temperature Speed Work Energy Charge Time Density