Forces Flashcards
Define mass and weight.
Mass- Amount of matter in an object.
Weight- The force with which the earth attracts a body towards its centre.
Give the formula for weight.
W= mg
Explain equilibrium.
When weight= resultant force and net force= 0.
Define inertia.
The tendency of an object to continue in its state of rest unless an external force is applied.
What’s momentum and the law of conservation of momentum?
The total momentum before and after the collision remain the same.
Give the formula for stopping distances.
Stopping distance= Thinking distance (0.2-0.9)+ braking distance
Explain the difference between distance and displacement.
Distance- Path between two points. (scalar)
Displacement- Shortest path between two points. (vector)
Define scalar and vectors.
Scalar- Quantity w/ magnitude.
Velocity- Quantity w/ magnitude + direction.
Define force.
A push/pull that acts on an object due to interaction with another object.
What can forces affect?
Shape, speed and direction
Describe the forces: weight, electrostatic, thrust and reaction force.
Weight- force of gravity on mass.
Electrostatic- Force between unlike charges.
Thrust- Any force causing an object to move.
Reaction force- A force due to contact between objects, force pairs.
Describe the forces:
air resistance, upthrust, compression and tension.
Air resistance- friction of air on moving object.
Upthrust- fluid pushing an object up to make it float
Compression- Force squeezing an object inwards.
Tension- Wire pulled by opposite ends.
What’s the difference between contact and non-contact forces.
Contact- forces between objects physically touching
Non-contact- forces acting at a distance.
Are forces scalar or vector quantities?
Vector they have magnitude (N) and direction (up/down/in angles)
What is a force pair and which of Newtons laws does it relate to?
Force pair- Interaction between two objects and a force is exerted on each object.. 3rd law: every action has an equal and opposite reaction.
What are the two method of measuring weight?
1- Find mass of object using a balance, then calculate.
2- Use a newton meter connected to a spring to hold the object.
Where is the center of mass?
Located at the point of symmetry, or at balance point. The point where the weight of the object acts.
How fast will a free falling object accelerate at towards the earth?
9.81 m/s^2
What’s a resultant force?
A single combined force that describes the action of all forces acting on an object. (determines magnitude and direction)
What are balanced and unbalanced forces?
Balanced- Forces cancel each other out, no resultant force.
Unbalanced- Forces combine, one force is greater than the others, this is the resultant force.
What are examples of forces acting on isolated systems?
Tension: force on rope when pulled.
Normal contact force: force that acts as object rests perpendicular.
Upthrust: upwards buoyancy on an object in a fluid.
Friction: Force when two surfaces are in contact.
What do resolving force diagrams represent?
If a force is acting at an angle, it can be broken down into two (horizontal and vertical)
What is work done?
Energy transferred when a force moves an object over a distance.
What is the formula for work done?
Force (N) x Distance (m)
Describe work done and friction’s relationship.
Friction will act in the opposite direction as motion of the object, it will slow it down.
What is friction?
The opposing force of an object moving in the opposite direction, slowing is down.
What other force is an example of friction?
Air resistance
How can you change the shape of an object?
Stretching, bending or compressing
What is meant by compression?
When 2 forces act in opposite directions towards the object.
What is meant by bending?
Two forces acting in opposite directions but one different points on the object.
What is the difference between elastic and inelastic deformation?
Elastic- will return to its original shape after force removed.
Inelastic- will not completely return to its original shape when force removed.
What is meant by elastic distortion?
Object remains permanently stretched.
What is Hooke’s law?
Extension of an object is directly proportional to force applied, until limit of proportionality is exceeded.
What is the formula for force? (Hooke’s law)
F= Spring constant (N/m) x extension (m)
For an object that follows Hooke’s law and and object that doesn’t, what would the graph look like?
Ext: x-axis
force: y-axis
Linear graph=Hooke’s law
Non-linear=Not Hooke’s law
RP6: describe the method to investigate the relationship between force and extention, to find if the spring follows Hooke’s law.
Set up apparatus: spring hanging from clamp n stand, measure initial length of spring, add masses and measure extension. repeat 3 times+find avg, calc force by W= mxg, plot ext and force see if follows Hooke’s law.
What is non-uniform motion?
When the movement of an object is always changing (direction or speed)
How do we use light gates to measure the speed?
Light gate will detect when an object passes through (since light is blocked) and starts a timer. Second light gate will stop the timer (when light is blocked)
Define velocity.
The speed of an object in a given direction (vector)
Describe velocity of an object moving in circular motion.
Even if speed is constant, the direction of an object is always changing because of circular motion and velocity is a vector quantity. This is non-uniform motion, and velocity is always changing.
How do we calculate speed from a distance-time graph?
gradient
What is instantaneous speed?
Speed at a particular moment in time.
How do we find instantaneous speed from an accelerating/decelerating graph?
draw a tangent at that point and calculate the gradient.
What is acceleration?
The rate of change of speed, how much velocity changes every second (m/s^2)
How do we find distance covered using a velocity-time graph?
Find the area under the graph.
give the (difficult) formula including acceleration.
v^2-u^2 / 2s = acceleration
v= final speed
u= initial speed
s= distance
Describe terminal velocity
The maximum speed of an object, its achieved when the forces moving the object are balanced by its frictional forces
What is Newton’s first law of motion?
Objects will remain at rest or in constant velocity unless acted on by a resultant force
How do we apply Newton’s first law?
A book rests on a table because weight=reaction force
What is Newton’s second law of motion?
The acceleration of an object is directly proportional to the resultant force acting on it, and inversely proportional to the mass of the object.
What is the formula for acceleration (easy)?
Force = mass x acceleration
RP7: Describe how changing the FORCE affects acceleration whilst there is constant MASS.
Method: Draw lines on a table every 0.2m until 1m. Add a 100g mass at the end of the pulley, let go so car moves. Record and find time taken between lines. Decrease the mass by 20g but add it to the car.
RP7: Describe how changing the MASS affects acceleration whilst there is constant FORCE.
Method: Draw lines on a table every 0.2m until 1m. Add a 100g mass at the end of the pulley, let go so car moves. Record and find time taken between lines. Add mass onto car to inc mass.
What is Newton’s third law of motion?
Whenever two objects interact the forces they exert on each other are equal and opposite.
What does the third law mean?
Forces act in pairs, force pairs are the same type.
How does the third law explain how we walk?
Foot pushes the floor backwards, the ground pushes the foot forwards.
What are the differences between law 1 and law 3?
1: No resultant force- balanced.
3: Two objects, one pushes and the other object the pushes itself in the opposite direction.
What is inertial mass?
The difficulty to change an object velocity. Higher inertial mass= greater force needed.
What is the formula for inertial mass?
Inertial mass= force/acceleration
What is stopping distance?
The total distance travelled during the time it takes for a car to stop in response to an emergency.
What is thinking distance and braking distance?
Distance covered during time taken for driver to react.
Distance covered under braking force.
What is reaction time?
A measure of how much time it takes for a person to react to something they see.
Describe a practical of how to measure reaction time.
Person A hovers ruler over Person B’s hand which rests on a table. Person A randomly drops the ruler for Person B to catch, this gives them a measurement.
What are the factors that affect reaction time?
Speed of car, intoxication, tiredness and distractions.
What are the factors that affect braking distance?
Vehicle condition, road condition, vehicle mass.
What is the relationship between braking and friction?
When a driver brakes, there is friction force between the brakes and the wheels of the car. The frictional force does work on the brakes and transfers energy. So kinetic energy falls but thermal energy rises. Car decelerates.
What is the equation needed to estimate decelerating forces?
Braking force x braking distance = Kinetic energy
What is the formula for momentum?
Momentum = mass x velocity
What is the conservation of momentum?
Total momentum before collision= Total momentum after collision
What is momentum affected by?
Mass, velocity and change in direction.
What is the (difficult) formula for momentum?
(MxV) - (mxv)= momentum
What is inelastic and elastic momentum?
Inelastic- Collide them move in same direction
Elastic- Collide and move in opposite directions.
What is perfectly inelastic and elastic collision?
Perfectly inelastic: Stick and move together
Perfectly elastic: Kinetic energy same before and after.
