Section 5: Mechanics Flashcards
What’s the difference between a scalar and a vector?
A scalar quantity has only size, while a vector quantity has size and direction.
What name is given to a vector formed by adding vectors together?
The resultant vector
Give an example of 3 vectors.
Displacement, velocity, force, acceleration or momentum
Give an example of 3 scalars.
Any 3 from: length, distance, speed, mass, temperature, time or energy
If a body is in equilibrium, what’s the sum of all the forces acting on it?
0
Explain what equilibrium means in the context of a moving object
The sum of all the forces acting on a body in equilibrium is 0
What is a moment?
A moment is the turning effect of a force around a turning point.
What name is given to a pair of forces of equal size which act parallel to each other, in opposite directions?
A couple
What is the centre of mass of an object?
The centre of mass of an object is the single point that you can consider its whole weight to act through
Where is the centre of mass in a uniform regular solid
At the centre of an object
What’s the velocity of an object?
The rate of change of displacement
What’s the acceleration of an object?
The rat of change of velocity
What does SUVAT stand for? Give the units for each measurement.
S- Displacement (in m) U- Initial Velocity (in ms^-1) V- Final Velocity (in ms^-1) A- Acceleration (in msˉ²) T- Time (in s)
What kind of motion does a curved displacement-time graph show?
Acceleration or deceleration
What kind of motion does a straight line show on a displacement-time graph?
Constant velocity
What does the rate of change of gradient on a displacement-time graph represent?
Distance
How would you calculate the average velocity of a moving object with non-uniform acceleration using a displacement-time graph?
Divide the overall change in displacement by the time taken
What is the difference between average and instantaneous velocity?
Instantaneous velocity is an object’s velocity at a particular moment in time, average velocity is the overall displacement divided by time taken
What does the gradient of a velocity-time graph tell you?
Acceleration
How is uniform acceleration shown on a velocity-time graph?
A straight line
What does the area under a velocity-time graph tell you?
The displacement
How is non-uniform acceleration shown on a velocity-time graph?
A curved line
How would you find velocity from an acceleration-time graph?
The area under the graph
How would constant velocity appear on an acceleration-time graph?
Constant velocity means acceleration is zero, so it would appear as a straight horizontal line through 0 on the vertical axis.
What does negative acceleration on an acceleration-time graph show?
Decleration
State Newton’s first law of motion.
“The velocity of an object will not change unless a resultant force acts on it.”
State Newton’s second law of motion
Newton’s second law states that the acceleration of an object is proportional to the resultant force acting on it. This can be shown as: F= m x a
F- Force (in N)
m- Mass (in Kg)
a- Acceleration (in ms^-2)
State Newton’s third law of motion
“If an object A exerts a force on object B, then the object B exerts an equal but opposite force on object A.”
What’s the only force present in free-fall motion?
Weight
What’s freefall motion called when the object is given an initial velocity
Projectile motion
What is the effect of air resistance on the trajectory of a projectile?
Air resistance causes a drag force that acts in the opposite direction to motion and affects the trajectory of a projectile, The horizontal component of drag reduces the horizontal speed of the projectile, and reduces the horizontal distance the projectile can travel. If the projectile has a vertical component of velocity, drag reduces the maximum height the projectile will reach, and steepens the angle of descent.
What is meant by friction and drag?
Friction is a force that acts opposite to motion. Drag is the name given to friction caused by a fluid.
In what direction does a frictional force act?
Opposite direction to motion
In what direction does a lift force act, relative to a flowing fluid?
Lift acts perpendicular to the direction the fluid is flowing
What can you say about the frictional forces and the driving forces acting on an object when it reaches terminal velocity?
When an object reaches terminal velocity, the frictional forces are equal in size to the total driving force and in the opposite direction
What is the difference between an elastic and inelastic collision?
An elastic collision is one where linear momentum and kinetic energy is conserved. An inelastic collision is one where linear momentum is conserved but kinetic energy is not
