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Flashcards in Physics - Forces And Newtons Laws Deck (24)

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



The measure of the amount of matter in an object

Measured in kilograms



The property of an object that describes how much it will resist change to the motion of the object

More mass = more inertia



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)



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



Pulling force exerted by the end of a string, rope, etc. on an object


Steps to tension problems (5)

1. Set forces in x and y equal
Ty + Ty = mg
Tx1 = Tx2

2. 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