Forces and Motion Flashcards
What is distance
Distance is the length of the path traveled during a journey
What is displacement
Displacement is the distance covered in a particular direction
What is the equation for average speed
Average speed = distance / time
What is the equation for average velocity
Average velocity = displacement / time
What is acceleration
Acceleration is the rate of change in velocity
What is the equation for acceleration
Acceleration = change in velocity / time taken
= final velocity - initial velocity / t
What is the gradient of a distance-time graph equal to
Speed
What does a horizontal line on a distance-time graph tell us
The object is stationary
What does a curve on a distance-time graph tell us
The object is accelerating
What is the gradient of a velocity-time graph equal to
The acceleration
What is the area of a velocity-time graph equal to
The distance traveled
What does a horizontal line on a velocity-time graph tell us
Constant speed
What does a downward line on a velocity-time graph tell us
Constant deceleration
What is the equation to find the displacement of an object moving with a constant acceleration
final velocity squared = initial velocity squared + 2 * acceleration * displacement
Is force a vector or a scalar
Force is a vector
What are the two types of forces
Contact forces and non contact forces
Name the different types of contact forces
Normal reaction force
Tension
Friction
Air-resistance
Upthrust
Thrust
Lift
What is the normal reaction force
The normal reaction force is the repulsive force that prevents two touching bodies from moving into each other. It acts at 90 degrees to the surface of the bodies
What is tension
Tension is the force that an object being stretched experiences. It acts along the direction of stretching
What is friction
Friction is the force that opposes motion between surfaces that slide past each other. The kinetic energy of the moving object is converted to heat by the force of friction
What is air resistance
Air resistance is the force that opposes the movement of objects through air. It increases with an increase in speed and surface area
What is upthrust
Upthrust is the upward force experienced by an object partially or fully submerged in a fluid. This is because greater pressure acts on its bottom surface than on its top surface which causes an upward resultant force
What is thrust
Thrust is the force that drives vehicles forward as a result of the expulsion of fluid in the opposite direction
Name the non-contact forces
Gravitational force / Weight
Magnetic force
Electrostatic force
What is weight
Weight is the gravitational pull of the Earth on an object towards the center of the Earth
What is mass
Mass is the amount of substance of an object
What is the equation for weight
Weight = mass * gravitational field strength
What is the resultant force
The resultant force is the single force that replaces all forces acting on a body
How do we calculate the resulatant force
Add together all the forces acting along the same direction and subtract the forces acting in opposite directions
What does Newton’s first law of motion state
An object will remain at rest or continue moving at a constant speed as long as the forces acting on it are balanced
What is Newton’s second law of motion
The acceleration of an object is directly proportional to the resultant force and inversely proportional to its mass
How is the acceleration of a body dependent upon the direction of motion
If the resultant force is in the same direction as the motion, the body will accelerate. If the resultant force is in the opposite direction to the motion, the body will decelerate
Write newton’s second law mathematically
Resultant force = Mass * acceleration
Explain how forces acting on a skydiver change his velocity as he falls from the helicopter to the ground
When the skydiver falls from the helicopter, his velocity is 0 m/s and the only force acting on him is his weight, causing him to accelerate very quickly downwards. However, as he accelerates and his speed increases, so does air resistance which acts in the opposite direction of motion, resulting in his acceleration to decrease. Eventually, the air resistance will balance out the force of the weight, resulting in the resultant force being 0 and consequently, according to Newton’s 1st law, the object will keep falling with a constant speed knows as terminal velocity. When the parachute is opened, the air resistance becomes much bigger due to the increase in surface area. Since it is greater than the weight and acting in the opposite direction of motion, the object will start to decelerate. However as its speed is decreasing so will the air resistance acting on the object, resulting in the deceleration becoming smaller and smaller. Eventually it will balance out the weight of the object and the parcel will consequently fall with a lower, constant speed
What is Newton’s third law
Every action has an equal and opposite reaction
What are the 5 conditions needed for two forces to form a newton third pair
Same size
Same type
Act in the same line of action
Act on two different objects
Act in the opposite direction
What is the thinking distance
The thinking distance is the distance covered during the reaction time of the driver
What is the braking distance
The braking distance is the distance covered after the driver has applied the brakes
What is the stopping distance
The stopping distance is the sum of the thinking distance and the braking distance
List the 5 factors that increase the thinking distance
Poor visibility
Driver is tired
Driver is distracted
Driver is influenced by alcohol
Speed (proportional to thinking distance)
List the 4 factors that increase the braking distance
Higher speed
Worn brakes
Mass of car
Road conditions
What happens to the thinking distance when the speed of the car is doubled
It is doubled
What happens to the braking distance when the speed of the car is doubled
It is quadrupled
What is elastic deformation
Elastic deformation occurs when a material returns to its original shape after the deforming force is removed
What is plastic deformation
Plastic deformation occurs when a material remains deformed after the force is removed
What does Hooke’s Law state
Hooke’s Law states that the extension of a material is directly proportional to the applied force, up to the limit of proportionality
What is the formula for Hooke’s Law
Force = k (stiffness) * extension
What does stiffness depend on
Material the spring is made form
Dimensions (length, thickness)
What is the limit of proportionality
The point above which the spring stops obey Hooke’s law as the force is no longer directly proportional to the extension
What is the elastic limit
The point above which the spring stops showing elastic behavior and it changes shape permanently
