Scalars and vectors, contact and non-contact forces, weight and mass, free body diagrams and finding a resultant force.
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1.What is a scalar quantity?
One that has magnitude only, with no direction.
2.What is a vector quantity?
One that has both magnitude and direction.
3.Give three examples of scalar quantities.
Speed, distance, mass, energy and temperature.
4.Give three examples of vector quantities.
Force, velocity, displacement, acceleration and momentum.
5.How is a vector represented in a diagram?
By an arrow whose length shows the magnitude and whose direction shows the direction of the quantity.
6.What is a force?
A push or a pull on an object caused by its interaction with another object.
7.What is a contact force?
One where the objects are physically touching, such as friction, air resistance, tension or the normal contact force.
8.What is a non-contact force?
One where the objects are physically separated, such as gravity, magnetic force or electrostatic force.
9.What is weight?
The force acting on an object due to gravity.
10.State the equation for weight.
weight = mass x gravitational field strength
11.What is the difference between mass and weight?
Mass is the amount of matter, measured in kilograms and the same everywhere. Weight is a force in newtons and depends on the gravitational field strength.
12.Calculate the weight of a 60 kg person on Earth, g = 9.8.
60 x 9.8 = 588 N.
13.Where does the weight of an object act?
At a single point called the centre of mass.
14.What instrument measures weight?
A calibrated spring balance, sometimes called a newtonmeter.
15.Why does an astronaut weigh less on the Moon?
The gravitational field strength on the Moon is much smaller, so the same mass has less weight.
16.What is a resultant force?
The single force that has the same effect as all the forces acting on an object combined.
17.Two forces of 8 N right and 3 N left act on an object. Find the resultant.
8 minus 3 = 5 N to the right.
18.Two forces of 6 N right and 6 N left act on an object. Find the resultant.
Zero. The forces are balanced.
19.What happens to a stationary object with zero resultant force?
It stays stationary.
20.What happens to a moving object with zero resultant force?
It carries on moving at the same speed in the same direction.
21.What is a free body diagram?
A diagram showing a single object with arrows representing all the forces acting on it.
22.What forces act on a car moving at constant speed?
The driving force forwards, and friction and air resistance backwards, which are equal in size so the resultant is zero.
23.How can a single force be resolved?
It can be split into two components acting at right angles to each other, usually horizontal and vertical.
24.How can two forces at an angle be added?
By drawing them to scale head to tail and measuring the resultant, using a scale diagram.
25.What does the normal contact force do?
It acts perpendicular to a surface, pushing back on an object resting on it.
26.An object rests on a table. Name the two forces acting and compare them.
Weight acting down and the normal contact force acting up. They are equal in size and opposite in direction, so the resultant is zero.
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