Physics - Forces And Newtons Laws Flashcards
Mass
The measure of the amount of matter in an object
Measured in kilograms
Newton’s first law
Law of inertia - an object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an unbalanced force
Inertia
The property of an object that describes how much it will resist change to the motion of the object
More mass = more inertia
Microwelds
Occur when two bumpy surfaces are rubbed up against each other
Newton’s second law?
F = m x a
Weight (force) =
Mass x gravity (earth)
Weight is a measure of the force of gravity on the mass of an object
Newton’s third law
For every action there is an equal and opposite reaction
Fn =
The normal force
The supporting force that acts in the object perpendicular to the surface plane. It’s the portion of the weight of the object that is supported
How to find friction force??
Ff = μFn
Ff = friction force (N) μ = coefficient of friction Fn = normal force (N)
Friction
The force that opposes motion between two surfaces that are touching each other
An object at rest has what kind of acceleration?
Acceleration is 0
If acceleration is zero…
Net force is equal to zero
Tension
Pulling force exerted by the end of a string, rope, etc. on an object
Steps to tension problems (5)
- Set forces in x and y equal
Ty + Ty = mg
Tx1 = Tx2 - Put Ty1, Ty2, Tx1, and Tx2 in terms of T1 and T2
T1sinθ + T2cosθ = mg
3. Set T1 in terms of T2 and Substitute
Because T1 = T2, this is possible.
Do T1sinθ1 + T1sinθ2 = mg
4. Solve for T1
5. Go back and solve for T2
T1 = (T2cosθ)/ cosθ
X =
Y =
X = cos
Y = sin
Inclined plane equations / reminders (4)
Fnet = mgsinθ - Fk Fk = μkFn
Fnet = mgsinθ - μkmgcosθ
Ma = mgsinθ - μkmgcosθ
A = sinθ - μkgcosθ
Tension problems equations / reminders (4)
Ty₁ + Ty₂ = mg
T₁sinθ + T₂sinθ = mg
Tx₁ = Tx₂
T₁cosθ = T₂cosθ (find T₁ and substitute for T₂)
Force problem equations and reminders (6)
Fx₁ = Fx₂ Fx₁ = F₁cosθ Fx₂ = F₂cosθ
Fnetx = F₁cosθ + F₂cosθ
Fnety = F₂sinθ + F₂sinθ
Above / below horizontal!
How do concussions occur?
The brain “floats” around in the skull, it will remain in its current state of motion until it crashes into the skull. The bruising of the brain is the concussion.
If a bug hits a car windshield, what are the forces exerted? Why is the car unaffected? What will happen to the cars acceleration at the time of impact? (3)
Bug and car exert equal forces
The windshield was made to withstand forces such as that
The acceleration will slight decelerate at the time of impact
How is it possible for a little boy to pull a wagon across his yard? Use Newton’s third law to explain
The boys feet push against the ground in the x-axis direction and the friction between the two surfaces allows the ground to “return” a lot of that force due to Newton’s third law
What are “Force pairs” and give an example.
Force pairs are action-reaction forces between two objects
Ex. Kicking a ball and you exert a force by your foot
The same force is exerted BY the ball ON your foot
If similar boxes slide down a ramp at the same angle, but one box has a little extra weight on it, what box slides down the fastest?
They both slide down at the same rate because the masses cancel out in the solving of the equations, meaning the mass is irrelevant
To prove that tanθ = μ (friction)… (6)
Fs = mgsinθ μFn = mgsinθ μmgcosθ = mgsinθ μcosθ = sinθ μ = sinθ/cosθ μ = tanθ
