3. Forces and pressure Flashcards
What is a force?
An influence which can
- change the state of rest or motion of a body
- change the size and/or shape of a body
- bring about turning effects in a body
- exert pressure on a body
What is the SI unit of force?
Newton.
What is used to measure a force?
A force meter, e.g. a spring balance.
What is mass?
Mass is a measure of the amount of substance in a body.
What is the SI unit of mass?
Kilogram.
What is used to measure mass?
Electronic or beam balance.
What is weight?
Weight is the gravitational force acting on a body.
What is the SI unit for weight?
Newton.
What is used to measure weight?
Extension or compression spring balance.
What is the formula for weight?
W = mg
What is the gravitational field strength for earth?
10N/kg
Differences between mass and weight
- Definition of mass and weight
- Mass is scalar whereas weight is vector
- SI unit for mass is kg; SI unit for weight is N
- Mass is constant regardless of GFS; weight varies according to GFS
- Mass is measured by electronic/beam balance; weight by extension/compression spring balance
What are the contact and non-contact forces?
Contact: friction, tension, normal contact force
Non-contact: gravitational force
Why doesn’t earth accelerate towards other objects on earth?
The mass of the earth is much larger than that of other objects, hence earth’s acceleration due to this force is negligible.
Explanation for GF
Gravitational force acts on the [object] by the earth in a downward direction, causing the [object] to accelerate vertically downwards.
Explanation for friction
Friction acts on the [object] by the floor to the [direction], opposes its motion and causes it to slow down and stop.
Explanation for tension
Tension in the string/cable/rope acts on the [object] vertically upwards.
What happens when the string is cut?
The [object] accelerates downwards. Tension is no longer exerted on the [object], so it’s weight provides an unbalanced force to change the motion of the [object].
Explanation for normal contact force
A normal contact force acts on the [object] by the floor vertically upwards.
What is resultant force?
Resultant force is the total of all the forces acting on a body, with both magnitude and direction considered.
What is gravitational field strength?
GFS is the amount of gravitational force acting on a body per unit mass.
What happens when a body’s acceleration is zero?
The body is in a constant state of motion.
If it was originally at rest, it will remain at rest; if it was originally moving then it will continue moving at a constant speed in a straight line.
When two or more forces produce a resultant force…
The forces are unbalanced.
What happens when there is resultant force?
The body will experience acceleration/deceleration/change in direction of movement, i.e. change in state of motion.
