Newtons law
the term that describes the attraction between two objects
What is Gravity?
This force pulls objects towards the Earth’s center.
What is gravitational force?
In a Free Body Diagram for an object moving at constant velocity, the net force must have this value.
What is zero?
The SI unit for force.
What is Newton (N)?
What is the difference between mass and weight?
Mass is the amount of matter; weight is the gravitational force on that mass.
Why does a passenger lurch forward when a car suddenly stops?
Inertia
This force opposes intended motion between surfaces in contact.
What is friction?
Forces balancing each other for an object resting on a flat surface.
What are normal force and gravitational force?
The net force on an object in mechanical equilibrium.
What is zero?
If the net force of an object is 0 then the object has to be at rest. Is this statement true?
no
A car with a mass of 1500 kg is accelerating at 2 m/s^2. What is the force acting on the car
3000 Newtons
What force always acts perpendicular to the contact surface and adjusts in magnitude to support an object in equilibrium?
What is normal force?
A correctly drawn Free Body Diagram includes these two fundamental properties for each force.
What are magnitude and direction?
A 15 kg object is pulled across a horizontal surface by a 60 N force at a 30° angle above horizontal. The coefficient of kinetic friction is 0.2. Calculate the object’s acceleration (use g = 9.8 m/s²).
What is approximately 1.90 m/s²?
Fx = 60·cos(30°) = 51.96 N
Fy = 60·sin(30°) = 30 N
N = mg - Fy = 147 - 30 = 117 N
f = μ·N = 0.2·117 = 23.4 N
F_net = Fx - f = 51.96 - 23.4 = 28.56 N
a = F_net / m = 28.56 / 15 = 1.90 m/s²
A spacecraft in deep space shuts off all engines. What happens to its motion?
moving at Constant velocity
An astronaut throws a wrench in space and starts spinning. Without touching anything else, how can they stop their own rotation? Which Newton’s Law applies?
Newton’s Third Law; they must throw another object in the opposite direction to conserve angular momentum.
Identify the type of force responsible for maintaining circular motion in objects attached to a rotating rope or string.
What is tension?
Explain why the normal force decreases when an inclined plane’s angle increases, despite the gravitational force remaining constant.
What is perpendicular force decreases?
A 10 kg mass is suspended by two ropes forming angles of 45° and 60° with the horizontal. Determine the tension in each rope (use g = 9.8 m/s²).
What are approximately 71.9 N (45° rope) and 50.8 N (60° rope)?
m = 10 kg
g = 9.8 m/s²
W = 98 N
Let T₁ = tension at 45°, T₂ = tension at 60°
T₁·cos(45) = T₂·cos(60)
T₁ = 1.414·T₂
T₁·sin(45) + T₂·sin(60) = 98
(1.414·T₂)(0.707) + T₂·(0.866) = 98
T₂(1.000 + 0.866) = 98
T₂ = 98 / 1.866 = 52.5 N
T₁ = 1.414·52.5 = 74.2 N
T₁ = 74.2 N
T₂ = 52.5 N
You jump straight up inside a train accelerating forward. Where do you land?
Behind start
A person is standing on a scale inside an elevator when the cable suddenly snaps, causing it to fall freely. and what does the scale read during the fall(person is still in contact with it?
zero
Explanation
The person remains in contact with the scale, but feels weightless because both are accelerating downward together, so the scale exerts no normal force.
Force type providing centripetal force for cars rounding flat curves.
What is static friction?
A ball is hanging from the ceiling of a bus by a string. The bus turns left at constant speed. In the bus’s frame, what three forces appear in the ball’s Free Body Diagram, and what is their direction?
Tension (toward right and up), weight (down), apparent force (left)
explanation
An apparent force is a fake force that seems to act on objects in an accelerating frame, used to make Newton’s laws work in that non-inertial perspective.
A 10,000 kg rocket ejects fuel at 3000 m/s at 5 kg/s. What is its instantaneous acceleration?
m·a = –v_e·(dm/dt)
a = (3000·5) / 10000 = 15000 / 10000 = 1.5 m/s²
A ball is dropped inside a rocket accelerating upward at 9.8 m/s² in deep space. What does the ball do relative to the rocket floor?
Hits floor
In the rocket’s accelerating frame, the ball appears to fall just like it would under gravity because the rocket floor accelerates up to meet it.