In free fall near Earth's surface, the velocity changes by how many m/s, downward, during each second of flight? Enter the number only.
Clara lifts a 12 kg bag of dog food onto a cart. Earth pulls down on the bag the whole time. That downward gravitational force is the bag's weight.
How big is that weight, in newtons?
You know what weight is: the gravitational force on an object. And a bigger mass means a bigger weight: a loaded backpack takes far more force to hold up than one apple.
One equation ties mass and weight together.
weight = mass × gravitational field strength
In symbols: w = mg.
The new name is the gravitational field strength, g. It measures how hard gravity acts at a place: the newtons of gravitational force on each kilogram of mass there.
Near Earth's surface, g is about 9.8 N/kg. That value says Earth pulls on each kilogram of mass with a force of about 9.8 N.
The units show the meaning: newtons = kilograms × newtons per kilogram. The kilograms cancel, and newtons are left.
So the bag's weight is 12 × 9.8 = 117.6 N, which is about 120 N.
A melon has a mass of 3.5 kg. Take g = 9.8 N/kg. Enter the melon's weight in N.
Near Earth's surface, how hard does Earth pull on each kilogram of mass?
Yusuf says: 'Two toolboxes with the same mass, sitting side by side in the same shop, have the same weight.' Is Yusuf correct?
One note on the symbol. Weight's symbol is a lowercase w. Later in the course, a capital W will name a different quantity, so the small letter matters.
The number 9.8 is one you have met before, in free fall.
As an acceleration, g says a falling object gains 9.8 m/s of downward velocity each second: g = 9.8 m/s².
As a field strength, g says Earth pulls on each kilogram with 9.8 N: g = 9.8 N/kg.
The two values are the same number. They are two readings of one g.
Clara's bag of dog food has a mass of 12 kg. Take g = 9.8 N/kg. Calculate the bag's weight.
Write down the values:
m = 12 kg, g = 9.8 N/kg, w = ?
Write down the equation:
w = mg
Substitute in the values, and calculate:
w = 12 × 9.8 = 117.6
The bag's weight is 117.6 N, about 120 N.
A basketball has a mass of 0.60 kg. Take g = 9.8 N/kg. Calculate its weight.
Write down the values:
m = 0.60 kg, g = 9.8 N/kg, w = ?
Write down the equation:
w = mg
Substitute in the values, and calculate:
w = 0.60 × 9.8 = 5.88
The basketball's weight is 5.88 N, about 5.9 N.
A full water bottle has a mass of 0.75 kg. Take g = 9.8 N/kg. Enter the bottle's weight in N.
Near Earth's surface, g is about 9.8 N/kg. Which statement says what that value means?
Near Earth's surface, g is 9.8 N/kg. Written as the free-fall acceleration, which value is the same g?